September 21, 2023 • 44 mins
Daniel and Jorge dust off their knowledge of the tiny-but-mighty grains of space dust which help form our world and block our view of the cosmos.
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Speaker 1 (00:08):
Hey, Daniel, you're kind of a neat freak, aren't you.
Speaker 2 (00:11):
I do like to keep my laptop nicely, well dusted.
Speaker 1 (00:15):
The weight dust it like you put dust in it,
or you take out dust, or you wipe dust out
of it.
Speaker 2 (00:20):
Good question. I mean, I like my cookies well dusted
with sugar, but my laptop keyboard well dusted with zero dust.
Speaker 1 (00:28):
Yeah, household dust is less delicious, and powdered sugar is
in regular dust, like fifty percent skin cells.
Speaker 2 (00:34):
That sounds like a pretty gross thing to put on
your cookies. On the other hand, it would be pretty
weird if powdered sugar just like accumulated in your.
Speaker 1 (00:41):
House, it'd be pretty sweet.
Speaker 2 (00:44):
We might call for some sweeping changes.
Speaker 1 (00:46):
Uh, I'm glad you got to dust off that old punt.
Speaker 2 (01:05):
Hi.
Speaker 1 (01:05):
I'm Poor hammy cartoonas and the author of Oliver's Great
Big Universe.
Speaker 2 (01:08):
Hi. I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I don't like dust as much
as astronomers do.
Speaker 1 (01:15):
But do you still like it a little bit?
Speaker 2 (01:17):
I like dust the way I like the sun. It's fascinating,
it's interesting, it's useful, It tells us about the cosmos.
But I don't really want it on my laptop or
on my table.
Speaker 1 (01:27):
But everywhere else it's okay.
Speaker 2 (01:29):
Yeah, study it from a distance, you know, the way
like I'm fascinated by cheetahs, but I don't really want
to have a cheat on my lap.
Speaker 1 (01:37):
Do you carry a duster with you at all times?
Speaker 3 (01:39):
Then?
Speaker 2 (01:39):
I actually do have this very fancy little machine for
removing dust from your keyboard.
Speaker 1 (01:44):
Is it called blowing on it? Or did you Did
you actually pay for a machine to do that?
Speaker 2 (01:48):
I actually have a nice little machine. It's really quite good. Yeah,
I should call it mini made.
Speaker 1 (01:52):
Wait, what is it like a vacuum?
Speaker 2 (01:54):
No, it's like a little blower, you know. It replaces
those disposable cans that I thought were not very environmentally friendly,
though I do love them.
Speaker 3 (02:00):
Mmm.
Speaker 1 (02:01):
Oh, I see you mean like the dust between the keys,
like you want to get rid of it, like in
the nooks and crannies.
Speaker 2 (02:07):
Yeah, exactly. I like a nice clean keyboard.
Speaker 3 (02:10):
Oh.
Speaker 1 (02:10):
I thought you meant like on your screen, because I
think you can just wipe that off.
Speaker 2 (02:13):
I think you can. But probably that dust contains all
sorts of fascinating stories where each of those bits has
been But you.
Speaker 1 (02:20):
Know, if you just blow the dust, it's just getting
in the air and then it's going to come back
down on your keyboard.
Speaker 2 (02:25):
I know it's a cycle. Unless I'm willing to live
in a clean room, I can never escape it.
Speaker 1 (02:29):
So you don't like living in clean rooms.
Speaker 2 (02:31):
I don't have to wear a hairnet and booties all
the time.
Speaker 1 (02:34):
No, just some of the time. But anyways, welcome for
a podcast Daniel and Jorge Explain the Universe, a production
of our Heart Radio.
Speaker 2 (02:43):
In which we dive deep into the cycles of the universe,
the ones that produce massive stars and tiny grains of dust.
Everything out there in the universe has a history and
tells a story, and if we can unpack it, unravel
it and study it, you can reveal those stories and
the history of our own cosmos. To learn about the
formation of the planets and stars and the universe itself,
(03:07):
from the biggest clues to the tiniest speck of dust.
Speaker 1 (03:10):
That's right, we blow the dust off of the universe,
trying to uncover what's underneath, What shiny surface or interesting
facts are there for us to understand and to learn about.
Speaker 2 (03:19):
I love in archaeology, how every time they're going to
discover something amazing, they always have to blow dust off
of it, pull cobwebs off of it. That's like your
visual cue that you're about to learn something ancient.
Speaker 1 (03:29):
Wait, wait, what do you mean?
Speaker 2 (03:30):
I mean? I just watched a new Indian Jones. I guess.
So you know anytime they unde earth something from the
olden days, it's always covered in dust.
Speaker 1 (03:37):
Of course, mm to see they carry a dust with
them at all times. Maybe you can buy one of
those devices and you didn't have to waste electricity.
Speaker 2 (03:46):
I'd be that neat freak archaeologist. I don't think i'd
get very far in the field.
Speaker 1 (03:50):
Yeah, it is a dusty universe full of amazing things,
where even the dust is interesting. In the universe.
Speaker 2 (03:55):
Down here on Earth we see dust is sort of
a nuisance, something to brush out of our But out
in space dust plays a very important role in the
formation of stars and planets, and it can reveal that history.
Dust is not just a nuisance. It's a fascinating pile
of tiny clues.
Speaker 1 (04:12):
So today end podcast, we'll be asking the question how
important is cosmic dust? Now? Hopefully this episode won't be
a bust.
Speaker 2 (04:27):
Should we just be sweeping cosmic dust under the cosmic
rug or should we take it seriously and study it
in detail.
Speaker 1 (04:34):
That's a bit of a dusty pun there, you used
it already, But yeah, it's an interesting question here cosmic dust.
I guess it's different than regular dust.
Speaker 2 (04:42):
Well, I think there's fewer dead skin cells and leftover
bits of insects out there floating between the stars than
there is here on Earth. But cosmic dust also falls
to Earth.
Speaker 1 (04:51):
You mean it gets sprinkled from space like powdered sugar.
Speaker 2 (04:54):
Well, you know that space isn't empty, and there's dust
out there between the stars but also between the planets,
and as the Earth moves through these cosmic dust clouds,
it accumulates some of them. Some tons of dust fall
to Earth every year from interplanetary space out there in
the Solar System.
Speaker 1 (05:09):
WHOA is it like dandruff space? Dandruff? Or is that
too embarrassing?
Speaker 2 (05:15):
We had a whole fun episode about where this stuff
comes from. It's a bit of a mystery. There's a
recent experiment though, that tries to pin the blame on Mars.
It might be that dust storms on Mars are blowing
that stuff out into space and the Earth is flying
through Mars's dust clouds. So yeah, I guess it's all
Martian dandruff.
Speaker 1 (05:32):
Yeah, Mars needs some head and shoulders.
Speaker 2 (05:36):
Well first they need heads and shoulders. That'd be pretty
awesome discovery.
Speaker 1 (05:39):
Yeah, or maybe just a hat that might help. But
it is an interesting question. How important is cosmic dust?
Which I guess means Daniel, that cosmic dust is important.
Speaker 2 (05:49):
Cosmic dust is more important than you might think. I mean,
the word dust makes you think it's insignificant. It's just
something to be blown off of. Something else. Man, it
gets in your way, something, it messes things up, something
to be gotten rid of. But dust has clues in it.
This is like the dust here on Earth tells you
who's been living there and the insects that have been around.
Dust out in space tells you what's been happening in
the universe, because there's dust makers and dust consumers, and
(06:11):
dust also plays a big role in making stars and planets.
Speaker 1 (06:15):
Well, you just said dust consumers out in space like
aliens who buy dust. That's what it sounds like.
Speaker 2 (06:22):
Not dust customers. You know, ways in which just is
created and then dust is destroyed. I should say dust destroyers.
Speaker 1 (06:29):
Oh there you go. See that's a device. I would
buy a dust destroyer.
Speaker 2 (06:33):
Wait till you learn how dust is destroyed. You don't
want one of these things?
Speaker 1 (06:38):
Maybe I do. Let's find out. Well, as usual, we
were wondering how many people had thought about the importance
of cosmic does and what role it has in our
search for the meaning of the universe and how it
all works.
Speaker 2 (06:49):
Thanks to everybody who pitches in for this segment of
the podcast. I hear from listeners that they really enjoy
hearing your voices in your thoughts on the episode topic.
If you would like to share your voice and thoughts,
please don't be shy. Write me to Questions at Daniel
Andandjorge dot com.
Speaker 1 (07:05):
So think about for a second, how important do you
think cosmic dust is. Here's what people have to say.
Speaker 2 (07:11):
Stop waving from the universe. I would say that twenty
percent is planet stars, black holes, sixty percent gus, and
the rest twenty percent is dust.
Speaker 3 (07:21):
I think that this is the one of those questions
that but you have to think about some things that
you usually take for granted. So I would say that
the QA is mostly composed by dust.
Speaker 1 (07:36):
All right, interesting, answers here, some people seem to interpret
the questions like how significant is cosmic? Doest?
Speaker 2 (07:45):
Yeah?
Speaker 1 (07:45):
Like, or like how much how much of the universe
is cosmic? Does?
Speaker 2 (07:49):
And they also seem to be taking it as a
leading question, like because I'm asking it, they're figuring probably
it's a big component of the universe and playing an
important role.
Speaker 1 (07:58):
I see, it wouldn't be very interesting just the answer
was just like not at all or nope, nobody cares.
Speaker 2 (08:05):
Yeah, Like how important are Daniel dirty socks?
Speaker 3 (08:08):
Yeah?
Speaker 2 (08:08):
Not interesting, not important? Move on, That wouldn't be a
very fun episode.
Speaker 1 (08:13):
Let's not talk about your socks because I know you
don't wear socks, so.
Speaker 2 (08:17):
Well, then it's a philosophy question, right can my socks
be unimportant if they don't even exist?
Speaker 1 (08:22):
There you go, philosophy of footwear.
Speaker 2 (08:25):
Somebody out there is doing a whole PhD thesis on
that topic, probably.
Speaker 1 (08:29):
On your socks. On socks, and Jackie, I know you're
famous now, Daniel, but geez.
Speaker 2 (08:34):
No on socks? Why they disappear where they go? Why
dryers consume them? See dryers are sock destroyers.
Speaker 1 (08:41):
Nay, it turns them into dust.
Speaker 2 (08:43):
Maybe it transports them to the hozone layer of the atmosphere.
Speaker 1 (08:45):
So let's dig into this topic, Daniel, what is cosmic dust?
Speaker 2 (08:50):
Cosmic dust is an important part of the Solar system,
though it's not a big fraction of the Solar system.
The answer from these listeners made me dig into the
question of like, actually, but is the mass budget of
the Solar system? How much of it is cosmic dust
and how much of it is made of other stuff?
Speaker 1 (09:08):
So what's the breakdown?
Speaker 2 (09:09):
So the Milky Way weighs about one to one and
a half trillion times the mass of the Sun. That's
like our mass unit a solar mass, and the total
Milky Way is about a trillion trillion and a half
solar masses. Now, most of that, like ninety percent of
that is dark matter. We know that the stuff that's
visible in the universe, the stuff that glows, and even
(09:30):
the stuff that doesn't glow that much, like rocks and
dust and asteroids, that's only like ten percent of the
mass of the Milky Way. Out there in the larger universe,
dark matter is a little bit less common than it
is here in the Milky Way. The Milky Way has
more dark matter than an average galaxy.
Speaker 1 (09:44):
And I guess. How do we know these things? Like
how do we know how much the Milky Way weighs?
Do we put it on a scale or something.
Speaker 2 (09:50):
We can measure the component of the Milky Way independently
and then add them up. The stars and the interstellar medium,
the black hole, all that stuff we can measure independently,
and then we can measure the total mass by looking
at how fast the Milky Way is rotating. Because stars
are like tracers, they move around the Milky Way, and
their speed is determined by the gravitational traction of everything
(10:12):
closer to the center than they are. Things further away
from the center on the outer shell don't affect them
at all, things on the inside do. So by reading
the speed of these stars, we can tell how much
mass they're radius encloses, and so that measures the total
mass of the Solar system. And that's how we infer
dark matter, sort of the left over bit that we
can't account for with stars and planets and gas and dust.
Speaker 1 (10:34):
But we can't see all of the Milky Way right
Like we're in the Milky Way, can we really see
the full extent of it and have a good guess
about its composition?
Speaker 2 (10:43):
There's a lot of uncertainty, which is why I said
one to one and a half trillion solar masses. So
that's like an uncertainty of five hundred billion solar masses.
And yeah, part of that comes from the fact that
we can't see the whole Milky Way because we're looking
through it, we're inside of it, and the Milky Way
has a good amount of dust in it, and that
dust obscures our view. So there's a whole region of
(11:03):
the Milky Way that we can't see very well in
many frequencies of light, and that leads to a lot
of this uncertainty. I see.
Speaker 1 (11:09):
So then how much of our Milky Way is dust?
Speaker 2 (11:12):
So it's like ninety percent dark matter, Then it's like
three percent stars, it's like one hundred to two hundred
billion stars. And then leftover is this stuff called the
interstellar medium, which is maybe like half a percent or
one percent of the mass of the Milky Way, and
one percent of that is dust. The interstellar medium is
mostly gas, it's like hydrogen and a little bit of helium.
(11:33):
So one percent of the interstellar medium, which is one
percent of the galaxy, is dust. So the dust is
like point zho one percent or maybe half of that.
It's a tiny fraction of the mass of the Milky Way.
Speaker 1 (11:44):
So I guess you don't count that gas is dust, right.
Speaker 2 (11:47):
That's right. And this is another example of humans putting
categories on things where really there's a smooth spectrum. If
we call it gas, it means it's like a molecule,
there's like h two floating out there, we call that gas.
If it's a larger clump of stuff, a bunch of
molecules together, little grains down like one hundred nanometers or larger,
we call that dust. Get much bigger, we start to
(12:09):
call you like a meteor or an asteroid or even
a planet. But in the end, there's a whole spectrum
all the way down from individual molecules which we call gas,
to larger clumps of stuff which we call dust, all
the way up to much bigger objects stars and planets.
Speaker 1 (12:24):
I guess at some point you get to like pebbles, right,
and little rocks. Is there such a thing as space sand?
Speaker 2 (12:32):
Well, you know this dust is made of carbon and silicates, right,
and sand is mostly silicates. So in the end, like
a lot of this space dust is kind of like
super fine grains of sand.
Speaker 1 (12:43):
But then I also imagine there is sort of sand
sized grains out there in space.
Speaker 2 (12:47):
There are larger pieces for sure, And so this intermedia
category we call dust is not a very big fraction
of the mass of the Milky Way. But to compare,
it's about the same mass as the central black Hole.
Point oh one percent of the Milky Way sounds like
a tiny number. It's a tiny percentage of a huge number, right,
one and a half trillion solar masses. So it comes
(13:07):
out to be about the mass of the central black Hole.
Speaker 1 (13:11):
And so where did all this dust come from? Like
are there giant space aliens shedding of their skin?
Speaker 2 (13:16):
To understand where the dust comes from, we need to
dig into a little bit more about like what is
this dust? And it's made of like a bunch of
different stuff, some tiny little portion of it, this is
really fascinating, comes from the atmospheres of stars. We know
that stars their job is to take hydrogen and helium
and lighter elements and fuse them into heavier elements, although
(13:38):
I have to iron and even heavier in the case
of supernova and in the atmospheres of these stars, especially
when they get really really big and near the end
of their life. Their atmospheres produce these little grains. They're
like coalesce as they cool, and the outflow in the
atmosphere of these stars. That's sort of like one source
of this stuff. But if you look out into the
universe and study this stuff, most of it is not
(14:00):
these presolar grains, these like pristine little blobs made in
the atmospheres of stars. Most of it's been like reprocessed,
like shattered and ground up and reformed into new bits.
Speaker 1 (14:10):
Interesting just from like the churning of space, of stuff
in space.
Speaker 2 (14:13):
Just from the churning of space. It turns out that
you can't just hang out as a grain in the
middle of space. There are processes happening out there. There
are processes that destroy dust and processes that reform it.
The dust destroyers that are out there. It sounds like,
you know, some big alien ship coming along to clean
up the universe, but actually it's shock waves from supernova.
When supernova collapse and then explode, they produce these huge
(14:37):
shock waves, massive amounts of energy, gamma, rays, neutrinos, all
sorts of stuff, and that comes along and it shatters
these grains, destroying the dust and breaking it like back
down into gas.
Speaker 1 (14:48):
Well you know they say space is just a big vacuum,
so those are just suckle. Anyways, So you were saying
that dust is important in the universe. Is it important
to the universe or just to our understanding or to
our search for answers about the universe?
Speaker 2 (15:04):
Well both, Like the history of dust tells us what's
happened out there in the universe. You can take each
individual solar grain if it survived this like interstellar shattering process,
and some of them have, and you can trace it
back to an individual star. Like every star has a
different mixture of elements and a different mixture of isotopes,
so they leave special fingerprints in their solar grains, and
(15:26):
so like ular grain can tell you, like what that
star was. It's like a little sample from that star.
And some of them are made during supernova and capture
elements and isotopes that only exist, we think, in the
atmospheres of supernova during those brief moments that are super
energetic and can tell us about the formation of heavy
elements and what's going on in supernova. So there are
(15:48):
these amazing capsules that tell us about the history of
the universe.
Speaker 1 (15:51):
But I think maybe you don't mean like each individual grain,
do you look? You maybe need like a population or
like a cloud of this dust to sort of know
what the star was like.
Speaker 2 (16:01):
Well, each individual grain tells you something about that star.
Not every grain produced by the star is identical, right,
and the star has a variety of stuff in it,
but each one traces back to an individual star.
Speaker 1 (16:12):
Just each grain would be made out of different things.
Speaker 2 (16:15):
Yeah, each star would make different kinds of grains. There's
going to be some overlap. It's not completely unique, right,
But each star is made out of different kinds of stuff,
different elements, different mixtures. Each star is a slightly different
mass and temperature and so produces different mixtures of stuff
and different isotopes, and so the grains produced by each
star are different.
Speaker 1 (16:33):
Like an individual grain would have different things in it
and different signatures in it.
Speaker 2 (16:38):
Yeah, exactly. The isotopes found in an individual grain tell
you about the star that it came from.
Speaker 1 (16:43):
Mmmm. Interesting, So how is it important to the universe itself?
Because it doesn't seem like it weighs a lot in
the Milca way, So maybe I wonder if it has
a big role in you know, the dynamics of space.
Speaker 2 (16:54):
It does play a big role in the dynamics of
space sort of for two reasons. One is that stuff
heavier than gas is the reason that we have like
planets and stars and stuff like that. Like the Earth
is mostly made out of stuff that's not just hydrogen
and helium, right, and that's cosmic dust gathered together to
form planets. So most of the rocky stuff of the
(17:15):
Solar system came originally from what we would call cosmic dust, right,
those heavier elements that are created by stars and spewed
out into space. And also we think that this cosmic
dust plays a role in the formation of solar systems.
You have a huge gas cloud that eventually collapses into
a bunch of stars. Why does it collapse. It collapses
because it's a little spot here that's denser, that's heavier,
(17:37):
that's cosmic dust. Man, Those are like the iron grains
and the little bits of heavy elements floating around that
seed that gravitational collapse.
Speaker 1 (17:46):
Wait, are you saying the Bible was right? We all
come from dust, from dust to dust.
Speaker 2 (17:50):
And even ashes, right, star ashes.
Speaker 1 (17:53):
Cool And so then how does it help us study
the universe or how does it not help us study
the universe.
Speaker 2 (17:58):
Yeah, it both hurts our ability to study the universe
and helps us. Like it prevents us from seeing things
in the universe because it absorbs light and it blocks
our view. The center of the Milky Way, which is
choked with dust, is famously called by astronomers the zone
of avoidance because they have to look away from that region.
You can't see through the center of the Milky Way
in optical lights, so you can't see what's on the
(18:21):
other side of the galaxy very easily. So it's sort
of a pain for astronomers, but it also captures this
history right, And in order to understand the cycles of
star formation in the universe, we do have to understand
the cosmic dust because the cosmic dust plays a role
in the formation of those stars and is also then
destroyed by the supernovas and then reforms. It's all part
of the cycle of the Milky Way. You might imagine
(18:42):
the Milky Way is just like a bunch of stars
floating in space basically doing nothing, but it's churning and burning.
This stuff going on just sort of much longer time
scales than we're used to thinking about.
Speaker 1 (18:53):
Hmm. Interesting all right, Well, let's get into how we
know where the dust in the universe is and the
very important question where does it all come from? Who's
making this mess in the universe. So let's dig into that,
But first let's take a quick break. All right, we're
(19:20):
talking about cosmic dust, which is not a drug, I imagine,
so it sounds like it might be something you'd sell
on the streets.
Speaker 2 (19:28):
I don't know. If you walk down the street in
Berkeley and you ask people for cosmic dust, I'm pretty
sure they'll sell you something.
Speaker 1 (19:33):
They'll sell you something. But we're talking about the dust's
out there in space between the stars, and it's important
because we're all made out of dust. Stars and planets,
they're all essentially come from dust that gravity pulls together,
and so it's important for that reason. But it also
sort of helps us understand the origins of stars in
the universe.
Speaker 2 (19:54):
Right, even though it's tiny, it's a little bitty part
of the mass budget of the Solar system. It tells
about how things work and it plays a role in
getting those things started.
Speaker 1 (20:03):
But I imagine maybe at some point in the universe's
history dust it was all dust, basically, right, That's where
all those stars came from No, I guess you went
from gas to stars and then those made dust exactly.
Speaker 2 (20:15):
We think that the universe began and dust lists right.
So it's actually an interesting open question in astronomy right now.
It is like when was the first dust made? People
really want to understand the process by which dust is
created and destroyed and helps form new stars, and there's
a lot of open questions out there. We don't really
fully understand the process of it. But we're pretty sure
(20:37):
that the universe began with just hydrogen and helium and
the tiny trace elements of things heavier and no larger
molecules of course, and it's only when stars began to
burn that dust was created.
Speaker 1 (20:49):
But I wonder if in the Big Band, you know,
things were so intense, there was so much pressure, there
was so much violent processes going on, so many of
those that I wonder if some hydrogens aret it e
merging together and make dust without any stars? Is that possible?
Speaker 2 (21:04):
With the earliest dust we've seen is like several hundred
million years after the Big Bang, and it's possible that
hydrogen formed and crystallized somehow earlier on. I don't think
we would call that cosmic dust. Though if it's just
pure hydrogen, probably you just call that hydrogen crystals. I
think to be called dust probably needs to have some
like carbon and some silicon and some heavier elements in it.
Speaker 1 (21:23):
But I mean, could a little bit of a carbon
and silicon have formed in the big during the Big Bang?
Speaker 2 (21:28):
Big Bang nuclear synthesis is a pretty precise science, and
it tells us, based on the temperature and like the
cork density, exactly how much of what was made. And
we think that it's almost overwhelmingly hydrogen, with just tiny
trace elements of helium and then little tiny, anty bitty
bits of heavier stuff carbon. Probably not because carbon requires
(21:49):
the merging of three helium simultaneously. Because lithium is so unstable,
so very unlikely that any carbon was formed, but you
can't say no, it's possible there were tiny, tiny grains
of carbon form during the Big Bang.
Speaker 1 (22:01):
So there could be primordial dust out there, like og dust.
Speaker 2 (22:05):
That's right, The most ancient dust is possible, though the
oldest dust we've ever seen is a few hundred million
years after the Big Bang.
Speaker 1 (22:13):
All right, Well, that brings us to our next question,
which is, how do we know where the dust in
the universe is. It doesn't glow in space, right, It.
Speaker 2 (22:19):
Actually kind of does glow in space, not the way
that stars do. Right. Stars create their own light through fusion.
They light up the whole universe. But everything out there
has a temperature, and everything that has a temperature glows.
Even the Earth glows. Right. It gives off infrared radiation,
and so dust glows in the very very infrared because
dust is pretty cold. So you can see the dust
(22:40):
if you use telescopes that can see infrared light and
so like the Spitzer Space Telescope and a James Web
Space telescope. These things out there can see dust in
our galaxy and in other galaxies by its thermal emissions.
Speaker 1 (22:54):
Like I guess you could tell where there was a
lot of dust and where there isn't a lot of dust.
Speaker 2 (22:57):
Yeah, exactly. You can't see an individual grain. You can
see like huge clouds of dust here and there. You
can see it glowing in the very far infrared. You
can also see dust by how it blocks light. Like
we think we understand how stars glow and the light
that they give off, and dust blocks that light. You know,
it absorbs some frequencies of it, it reflects other frequencies of it,
(23:18):
and so by looking at what astronomers call the extinction curve,
like where's light being blocked, they can measure how much
dust there is between us and something.
Speaker 1 (23:27):
So we measure it by how it much it blocks light,
not how much it reflects light.
Speaker 2 (23:31):
We measure it by how much it blocks light and
also emits a little bit of light in the infrared,
so it depends a lot on the frequency it will reflect.
Blue light mostly infrared light can mostly pass through dust
shorter frequencies where the light has like roughly the wavelength
of the dust that will get reflected or absorbed. So
when light passes through a dust cloud, it basically gets
reddened because the blue light gets reflected and the red
(23:55):
light makes it through.
Speaker 1 (23:57):
It's a little bit of the opposite of what happens
here during the sunset. No, it's the same.
Speaker 2 (24:00):
It's the same. The light gets reddened, right, the atmosphere
tends to reflect blue light, so the sky looks blue
because in direct sunlight it's scattered down to your eye.
That at sunset, the light is coming straight at you
and the blue light is being reflected away and you're
seeing the red light. Mm.
Speaker 1 (24:15):
It filters like it filters out blue light.
Speaker 2 (24:17):
M hmm, exactly, it filters out blue light. And so
when astronomers look out into the sky, they can see
that some stars appear to be dimmed, and they appear
to be dimmed differently across the spectrum. Right, It's not
just like the whole star is dimmer, which might mean
it just further away, but it's dimmed more in the
red than in the blue. So these extinction curves are
really important for astronomers to study because every time they're
(24:39):
looking at something in the universe, they want to know,
like how much dust are we looking through? How much
is dust distorting what we're seeing?
Speaker 1 (24:46):
So technically, does that mean that dust, this space dust
is blue like if you were well, when you sort
of look at it, it's blueish.
Speaker 2 (24:53):
I guess it reflects blue light. It glows in the
far infrared, but it reflects blue light, so I guess
that would make it kind blue.
Speaker 1 (25:00):
Yeah, And have we ever like got in a sample
of dust, Like, have we ever gone out there and
grabbed a you know, vacuum up some dust to study it?
Speaker 2 (25:09):
We do actually have samples of space dust. It's super fascinating.
All the dust that we have sampled is only stuff
in our solar system, so we've never sampled stuff outside
of our solar system. The furthest probes we ever sent
have like just barely left the Solar system. But there's
plenty of space dust here in our solar system, and
many many satellites that we send have little dust collectors.
(25:30):
It's kind of a challenge because these satellites are moving
in very high speeds relative to the dust, so it
can be trickyed like catch the dust. But there are
some missions like the Star Dust Mission, specifically to capture
dust and bring it back, But then lots of other
satellites have like a little space dust collector on it.
We talked once about the JUNO mission that went to
Jupiter in twenty eleven had sort of an accidental star
(25:51):
dust collector on it. The dust was slamming into the
back of the solar panels on the satellite and then
spilating off little bits which you got picked up by
a camera, and it turned out to be like a
huge effective dust collector, and this is how we learned
that Mars is giving off all of this dust, which
is probably responsible for causing the zodiacal light. We have
(26:11):
also captured some dust and broad down to Earth and
studied it under a microscope and seeing like some fractions
of this stuff really are presolar grains, bits of dust
that are older than our solar system. Oh, super old dust,
super old dust. Our solar system is like four and
a half billion years old. But of course stars have
been around for much longer than that, and some of
(26:31):
them died and created these grains, which amazingly survived out
there in space and then formed into asteroids or formed
as part of the Earth, or still just floating out there.
It's incredible that some of these little grains have lasted
so long.
Speaker 1 (26:45):
And we also know how much dust is out there
because it's polarized, right, It's got some sort of electrical charge,
noess to it.
Speaker 2 (26:52):
Yeah, the dust grains are not spherical, right, They have
little shapes. They're irregular, which means that they tend to
be longer in one direction than another. And because they're
made of electromagnetic stuff, sometimes they have an overall charge.
You know. The dust like bumps against itself, it gets
like static electricity essentially, and then interstellar space it will
align with magnetic fields, you know, the Earth has a
(27:13):
magnetic field, the Sun has a magnetic field, the whole
galaxy has magnetic fields. We think there might even be
magnetic fields out there in between superclusters. We talked once
about primordial magnetic fields. Anyway, the dust grains are a
great way to measure those magnetic fields because they align
with the magnetic fields, and then when light passes through them,
it tends to polarize the light because the dust itself
(27:35):
is pointing in a specific direction. So light passing through
this region can tell you about the dust and about
the magnetic fields in that region. It's sort of an amazing
way to like learn about these huge regions of space
which otherwise look empty.
Speaker 1 (27:48):
Well, it's like having special glasses to see the universe.
Speaker 2 (27:51):
Yeah, exactly. So we have lots of ways to study
cosmic dust and to look at the spectrum. And you know,
looking at the spectrum also tells you what's in there,
because if it has like a certain crystal, then that
crystal has rotational and vibrational frequencies and they will absorb
with those frequencies or emitted those frequencies, and so they
can tell what's in cosmic dust. Even if we can't
(28:11):
sample it, like cosmic dust is far far away in
the milky Way. They can tell what it's made out
of based on how it glows and how it absorbs light.
Speaker 1 (28:19):
Hmmm, because that can change, I guess, depending on what
was happening there that made the dust exactly.
Speaker 2 (28:26):
Because cosmic dust is not static, right. One of the
big mysteries is like where's all this cosmic dust come from?
And you know, we think that a lot of it
is made in stars. It's made in supernova, It's made
in these stars called asymptotic giant branch stars. It's made
in super red giant stars to have like just the
right conditions in their atmosphere to coalesce this stuff, like
(28:48):
outflowing and cooling gases will create these grains and shoot
them out into the universe. And that's cool, but it
can't explain all the dust that we see out there.
There's like not enough stars and not enough for of
this dust to explain all the dust that's out there
in the universe. Because, as we said earlier, the dust
doesn't survive forever. Right. The dust is like shattered by supernova.
(29:09):
So we have like stars pumping dust out in the
universe supernova shattering it back in the gas, and that
leaves sort of a mystery because there's not enough being
made by the stars to explain all the stuff that
we see out there, all the dust in the Milky
Way I see.
Speaker 1 (29:21):
So like dust is sort of like they're bigger molecules basically, right,
they're like little tiny pebbles, and inside of the stars
they just burn up I guess, right, because it's so
hot and under so much pressure.
Speaker 2 (29:33):
Yeah, that's why they're made. Like in the outer atmosphere,
the outflowing and cooling gases coalesced into these grains. If
that ever happened inside the star, that would just burn
up as fuel.
Speaker 1 (29:42):
Yeah, like the carbon and all the silicon. It's sort
of gassy within the sun, but once it gets out
of the Sun, it tends to form into molecules and
maybe little clumps mm hmm. But then you're saying like,
once it's out there in space, then if there's a supernova,
the supernova breaks it up back into carbon and silicon exactly.
Speaker 2 (29:59):
So like the typical lifetime for a grain of dust,
it's like one hundred million years. It can float out there,
and then on average it's going to get shattered after
about one hundred million years, some longer, some shorter, but
on average one hundred million years.
Speaker 1 (30:12):
There are that many supernovas happening that to shatter does
so frequently.
Speaker 2 (30:16):
There are not that many supernovas, but they're frequent enough
and powerful enough to shatter this cosmic dust.
Speaker 1 (30:22):
So like on average, for any point in space, you
experience this shattering supernova every hundred million years.
Speaker 2 (30:28):
Yeah, the supernova are more common than every hundred million years.
There's a supernova in our galaxy roughly every fifty years,
so in one hundred million years, you're going to get
two million supernova across the galaxy and they're very very powerful.
So the modeling at least tells astronomers that these things
should be shattered on average within one hundred million years.
Speaker 1 (30:48):
But the Earth has been around longer than that, and
have we experienced such as shattering supernova.
Speaker 2 (30:53):
The Earth has been around much longer than that, but
it would take a very close by supernova to shatter
the Earth. These grains are more delicate than Earth, which
has been like compressed right.
Speaker 1 (31:02):
M So like if there's a bit of dust circling
the Earth, it would get shattered by the supernova, but
not our atmosphere or US.
Speaker 2 (31:09):
Yeah, dust is more fragile. You know, it's floating out
there into space. It's very low pressure. These things are
sort of fragile compared to like a rock on Earth.
Speaker 1 (31:16):
All right, So then the mystery you're saying is like
how it's made?
Speaker 2 (31:20):
Then, Yeah, the mystery is like why is there still
so much of it? There's a lot more cosmic dust
out there than can be explained by this combination of
stars producing it and then supernova's destroying it. There's a
lot more cosmic dust that can be explained by just
that process.
Speaker 1 (31:34):
Maybe the unergy just hasn't bought that neat device you
have to get rid of dust.
Speaker 2 (31:40):
Well, one theory about what's going on is that cosmic
dust itself can reform out there between the stars. So
you take these little pebbles, these little grains, you send
them out there. They get shattered back into gas, but
there's like a tiny little seed left, you know, a
few molecules still cleaning together, and then those can accrete
because they're flowing through these molecular clouds which are super
(32:02):
duper cold, and basically because you have a few tiny,
little grains left, they can like pick up more like
ice can form on these things, and you get these
layers that surround the original tiny core that rebuilds this
thing back up into what you would call dust.
Speaker 1 (32:18):
I see. Yeah, just reforms because and also because of gravity.
I imagine, right, like even if you split a little
grain of dust out there, eventually, gravity is going to
put it back together, isn't it.
Speaker 2 (32:28):
Yeah, exactly? And you know that's the process that eventually
forms stars and planets, right, These little gravitational seeds gathered
together over very long periods, but it begins with gathering
little bits of ice here and there and reforming. And
so some of the cognic dust that's out there are
like og grains that came from their stars and haven't
(32:49):
been shattered, but most of it probably comes from this
process where they have been shattered and then they coalesce,
collecting ice and reforming into grains.
Speaker 1 (32:58):
All right, Well, you mentioned that there are some things
called dust destroyers out there in space and also mysterious
ways that dust is made, and so let's dig deeper
into those things. But first let's take a quick break. Okay,
(33:23):
we're talking about dust and Daniels you're saying, the big
question is where does it come from? Because most of
the dust. If you just put dust out there in space,
within one hundred million years, some distant supernova's shockwave is
gonna shatter that back into its constituent atoms like carbon
and slogan. It doesn't seem that fragile here on Earth, right,
Like if I blow on dust, it doesn't break up
(33:44):
into carbon gas.
Speaker 2 (33:46):
I mean, you're pretty tough, dude, But are you saying
that your breath is as powerful as a supernova?
Speaker 1 (33:50):
Well, some mornings, yeah, But I mean, like it's weird
to think that it's so powerful because here on Earth
we don't feel these supernovas. But you're saying it's drying
enough to like split apart molecules in space.
Speaker 2 (34:02):
The dust is more fragile than the Earth is. Yeah,
and it hasn't been a supernova in our Milky Way
in quite a few hundred years, so it's not like
we're feeling these things every ten years or so. Even
these supernovas are not that common. But yeah, the lifetime
of dust is shorter than the lifetime of the Earth.
So the Earth and planets and stars definitely survived these
super nova shock waves in ways that the stellar dust doesn't.
Speaker 1 (34:25):
So then the mystery is, like, if it is being
destroyed out there in space, why is there still dust?
Why is in and auges gas and individual atoms exactly?
Speaker 2 (34:35):
And it's important that the dust is there because the
dust seeds planetary formation and star formation, you know, in
ways that we didn't always understand. Like back in the seventies,
before we really understood cosmic dust at all, people thought
that our solar system started just from gas, that you
could start from just like a blob of hydrogen and
helium and form all of this stuff, which doesn't really
(34:56):
make sense to me because then like where you're getting
all the iron and all this stuff to make planets.
But now it's very well understood that most of the
iron and most of the heavy metals are bound up
in these cosmic dust grains and you need them to
form solar systems with interesting bits on them like rocks
and people.
Speaker 1 (35:14):
So then are you saying that like just gravity, you know,
pulling all of this stuff out there floating in space
into dust is not enough to account for the dust
we're seeing, Well, why not?
Speaker 2 (35:23):
So just stellar production of dust isn't enough to account
for the dust that we're seeing. You need some way
to reform dust in the interstellar medium, otherwise, as you say,
it would be just gas. But we think that these
little grains probably do gather back together from gravity and
from deecretion of ice crystals. As you pass through a
molecular cloud, there's going to be chemical bonds that form
because these things are a little sticky, right, And so
(35:46):
that is a process that they think might explain where
the gas comes from. I talked to one scientist at
the University of Wasita in Japan who's super interested in
cosmic dust, and she said that this is like the
leading theory for how cosmic dust is being regenerated. But
nobody's like demonstrated this in the lab. They haven't done
tests where they take like a little grain and pass
(36:07):
it through a dust cloud and see this stuff reform.
It's alsort of like theoretical chemistry at this point.
Speaker 1 (36:13):
Well, you need to replicate zero gravity, wouldn't you.
Speaker 2 (36:16):
Yeah, exactly. It's the kind of experiment you'd want to
do out in space or on the iss or something.
Speaker 1 (36:20):
So then that's the best answer to this mystery.
Speaker 2 (36:23):
That's the best answer to this mystery.
Speaker 1 (36:24):
So it sounds like you're saying, like there's a giant
vacuum in space just gathering all this stuff dust.
Speaker 2 (36:31):
Well, you know again it's the supernova, right, Those are
the dust stories shattering it back into gas, and then
they think that it's probably reforming. But another really fascinating
way that they're trying to understand this process is by
trying to answer a related question, which is like how
early did dust form in the universe. So now that
we have like a super powerful infrared telescope, we can
(36:51):
look deeper into the history of the universe and look
for evidence of dust very very early on, like what
is the oldest dust that we can see in the universe,
and they'll give us a sense for these processes because remember,
like stars didn't turn on for a few hundred million years,
so the origin of the dust can really tell us
about like who is making this dust?
Speaker 1 (37:10):
Right I think I mean, like if you look out
into deep space with your telescopes, you're looking back in time,
so like the light you're getting from those deep places
in the universe is really old light, which might be
old dust exactly.
Speaker 2 (37:24):
And we think that most of the dust out there
in the universe right now is probably produced by these
super red giant stars and this asymptotic giant branch stars.
These special stars are super big and have just the
right conditions for this, like outflowing gas to cool and
form these little blobs which then flow down into space.
But the James Web Space Telescope recently saw direct evidence
(37:44):
for really really old grains of stars, like several hundred
million years or up to a billion years after the
Big Bang, too long ago for these stars, Like, we
don't think that there were these super red giant stars
early on in the universe. So probably the first dust
made in the universe were made by supernova from the
first generation of stars.
Speaker 1 (38:06):
WHOA wait, so how do we know we're looking at
dust that old.
Speaker 2 (38:11):
Because we're looking at images of galaxies that are super
duper far away. And so you can look at a
galaxy and you can understand from its red shift how
fast it's moving away from us, and therefore how far
away it is, and therefore the age of the thing
we're looking at.
Speaker 1 (38:24):
Isn't most of that light coming from the stars in
the galaxy.
Speaker 2 (38:27):
Yeah, most of that light does come from the stars,
But we're looking at an infrared telescope, and stars are
much quieter in the infrared, so we're seeing information from
the dust also.
Speaker 1 (38:36):
Oh, I see, like we see the galaxy with a
regular light and then we switch the filter over to infrared,
and then you're basically getting the light from the dust.
Speaker 2 (38:45):
Exactly, and specifically, what they're seeing here is extinction, right.
They're seeing an absorption feature at a very specific wavelength
twenty one seventy five inkstrums that they think is like
a dust wavelength, that that's what dust absorbs. So they
see like a dip in the light in this galaxy
at just the right wavelength that tells them that there
is dust in this very very old galaxy.
Speaker 1 (39:06):
Oh, because I guess the size of your thing affects
what kind of light you're absorbing, right, because you kind
of have to be at about the same size as
the wavelength to absorb it exactly.
Speaker 2 (39:17):
Earlier we were talking about how dust absorbs as various frequencies.
In general, the picture is that it interacts more with
blue light. It reflects that blue light, and it doesn't
interact as much with redor light because, as you say,
it's too small, like the wavelength of light is bigger
than these dust grains so it doesn't interact with them.
But also these things contain specific chemicals and sometimes little crystals,
(39:39):
and those have features that absorb at certain wavelengths, like
little oscillations and vibrational energy levels of these little crystals
inside these dust grains will absorb at specific wavelengths that
are known to be dust wavelengths. So they saw this
in this signature from the James Web Space telescope from
the duper Ancient galaxy, a galaxy too old to whole
(40:00):
any of these red giant stars or ASB stars. So
they think probably this is ancient dust, maybe from the
first round of generation of dust in the universe, probably
from supernova.
Speaker 1 (40:12):
Like the first supernova's right, because that's that's when the
heavier elements are made.
Speaker 2 (40:16):
And it's fascinating because supernova make this stuff and then
also destroy it, so they kind of like clean up
after themselves.
Speaker 1 (40:23):
Right, Wait, how can it make them and destroy them
at the same time.
Speaker 2 (40:25):
These dust grains are made by supernovas sort of in
the last dying minutes of a star's life, where you know,
these shockwaves create really intense environments and specific isotopes, and
then the outflow and the cooling makes these grains, but
then shockwaves from supernova's also destroy dust. Right, supernova are
the dust destroyers of the universe, So they both create
it and they also are responsible for destroying it.
Speaker 1 (40:46):
Which do they do first? Do they first clean up
and then put a bunch of dust there or do
they put a bunch of dust and then immediately destroy it.
Can't be the latter, can it, because then we wouldn't
have any dust.
Speaker 2 (40:55):
It must be that the shockwave from the supernova travels
out faster than dust grains, which means the first they're
cleaning up and then they're making a mess. So I
guess you're right. Actually it's in the wrong order. Or
they're destroying the dust grains from other supernovas and to
make space for their own.
Speaker 1 (41:10):
So they're not cleaning up after themselves. They're just cleaning
it so that they can make a mess.
Speaker 2 (41:15):
Yeah, they're sort of like scrubbing the graffiti off the
wall and then writing their own name on it.
Speaker 1 (41:20):
Yeah.
Speaker 2 (41:23):
I take it back. I take back everything positive I
said about supernovas well.
Speaker 1 (41:26):
They're the reason we're here, so glad they haven't wiped
us off. I guess I'm we're glad that they made us.
All right, Well, what does it all mean about our
understanding of the history of the universe.
Speaker 2 (41:39):
It means that all these processes, the ones that form stars,
that lead to supernovas, that lead to dust creation and
dust destruction, it's all part of this huge cosmic dance.
You know. We tend to think of the Milky Way
as like done, We've made all these stars. They're just
sort of like hanging out and burning now. But it's
a process, you know, and everything is connected as like
dust flowing and swirling. These things are being created, they're
(42:01):
being destroyed, they're being reformed. The whole thing is a big, frothing, active,
lively mess of processes, all of which are important to
creating the universe as we know it.
Speaker 1 (42:10):
Yeah, and it sounds kind of precarious, right, Like basically,
we need a supernova to make all this dust, and
we need the dust to basically clump together into planets
and stars quickly before the next supernova tries to wipe
the board clean. Right, Like if another supernova had gone
off near us, or not even neros, but around us,
(42:31):
before the Sun, you know, got put together and the
Earth got put together, we might not be here. Is
that true?
Speaker 2 (42:37):
It definitely would have affected things, but it's not something
we understand very well. And supernova's contribute in lots of
different ways. Like first of all, they destroy these grains,
but then later on a supernova shockwave can actually precipitate
the gravitational collapse of surviving grains into a new star.
So supernova shockwaves play lots of different complex roles. And
(42:58):
to say like that we even understand this story would
be to overstate it. For sure, there's a lot of
parts of this that we still don't understand. What we
do know is that it's complicated and everything is connected.
Speaker 1 (43:08):
Sounds like our knowledge of it is a little dusty.
Speaker 2 (43:12):
There's definitely a lot of ancient wisdom out there we
haven't yet collected, and we can look forward to blowing
the dust off of all of these.
Speaker 1 (43:18):
Secrets, but not too hard, because then you might destroy
the dust.
Speaker 2 (43:21):
Right, only if you have supernova morning breath.
Speaker 1 (43:24):
All right, I guess the next time you look at
into the nice guy, I know that you're looking at
a bunch of dust as well, not just the beautiful
twinkling stars.
Speaker 2 (43:31):
These tiny but mighty grains play an important role in
the formation of the Solar system, in helping us understand
what's out there, and also in blocking our view of
part of the glorious cosmos.
Speaker 1 (43:43):
Hope you enjoyed that. Thanks for joining us. See you
next time. Hey, it's hoar Hey from the podcast, and
I'm super excited to announce that my new book, Oliver's
Great Big Universe, is available to order now.
Speaker 2 (44:02):
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Hey, Daniel, you're kind of a neat freak, aren't you.
Speaker 2 (00:11):
I do like to keep my laptop nicely, well dusted.
Speaker 1 (00:15):
The weight dust it like you put dust in it,
or you take out dust, or you wipe dust out
of it.
Speaker 2 (00:20):
Good question. I mean, I like my cookies well dusted
with sugar, but my laptop keyboard well dusted with zero dust.
Speaker 1 (00:28):
Yeah, household dust is less delicious, and powdered sugar is
in regular dust, like fifty percent skin cells.
Speaker 2 (00:34):
That sounds like a pretty gross thing to put on
your cookies. On the other hand, it would be pretty
weird if powdered sugar just like accumulated in your.
Speaker 1 (00:41):
House, it'd be pretty sweet.
Speaker 2 (00:44):
We might call for some sweeping changes.
Speaker 1 (00:46):
Uh, I'm glad you got to dust off that old punt.
Speaker 2 (01:05):
Hi.
Speaker 1 (01:05):
I'm Poor hammy cartoonas and the author of Oliver's Great
Big Universe.
Speaker 2 (01:08):
Hi. I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I don't like dust as much
as astronomers do.
Speaker 1 (01:15):
But do you still like it a little bit?
Speaker 2 (01:17):
I like dust the way I like the sun. It's fascinating,
it's interesting, it's useful, It tells us about the cosmos.
But I don't really want it on my laptop or
on my table.
Speaker 1 (01:27):
But everywhere else it's okay.
Speaker 2 (01:29):
Yeah, study it from a distance, you know, the way
like I'm fascinated by cheetahs, but I don't really want
to have a cheat on my lap.
Speaker 1 (01:37):
Do you carry a duster with you at all times?
Speaker 3 (01:39):
Then?
Speaker 2 (01:39):
I actually do have this very fancy little machine for
removing dust from your keyboard.
Speaker 1 (01:44):
Is it called blowing on it? Or did you Did
you actually pay for a machine to do that?
Speaker 2 (01:48):
I actually have a nice little machine. It's really quite good. Yeah,
I should call it mini made.
Speaker 1 (01:52):
Wait, what is it like a vacuum?
Speaker 2 (01:54):
No, it's like a little blower, you know. It replaces
those disposable cans that I thought were not very environmentally friendly,
though I do love them.
Speaker 3 (02:00):
Mmm.
Speaker 1 (02:01):
Oh, I see you mean like the dust between the keys,
like you want to get rid of it, like in
the nooks and crannies.
Speaker 2 (02:07):
Yeah, exactly. I like a nice clean keyboard.
Speaker 3 (02:10):
Oh.
Speaker 1 (02:10):
I thought you meant like on your screen, because I
think you can just wipe that off.
Speaker 2 (02:13):
I think you can. But probably that dust contains all
sorts of fascinating stories where each of those bits has
been But you.
Speaker 1 (02:20):
Know, if you just blow the dust, it's just getting
in the air and then it's going to come back
down on your keyboard.
Speaker 2 (02:25):
I know it's a cycle. Unless I'm willing to live
in a clean room, I can never escape it.
Speaker 1 (02:29):
So you don't like living in clean rooms.
Speaker 2 (02:31):
I don't have to wear a hairnet and booties all
the time.
Speaker 1 (02:34):
No, just some of the time. But anyways, welcome for
a podcast Daniel and Jorge Explain the Universe, a production
of our Heart Radio.
Speaker 2 (02:43):
In which we dive deep into the cycles of the universe,
the ones that produce massive stars and tiny grains of dust.
Everything out there in the universe has a history and
tells a story, and if we can unpack it, unravel
it and study it, you can reveal those stories and
the history of our own cosmos. To learn about the
formation of the planets and stars and the universe itself,
(03:07):
from the biggest clues to the tiniest speck of dust.
Speaker 1 (03:10):
That's right, we blow the dust off of the universe,
trying to uncover what's underneath, What shiny surface or interesting
facts are there for us to understand and to learn about.
Speaker 2 (03:19):
I love in archaeology, how every time they're going to
discover something amazing, they always have to blow dust off
of it, pull cobwebs off of it. That's like your
visual cue that you're about to learn something ancient.
Speaker 1 (03:29):
Wait, wait, what do you mean?
Speaker 2 (03:30):
I mean? I just watched a new Indian Jones. I guess.
So you know anytime they unde earth something from the
olden days, it's always covered in dust.
Speaker 1 (03:37):
Of course, mm to see they carry a dust with
them at all times. Maybe you can buy one of
those devices and you didn't have to waste electricity.
Speaker 2 (03:46):
I'd be that neat freak archaeologist. I don't think i'd
get very far in the field.
Speaker 1 (03:50):
Yeah, it is a dusty universe full of amazing things,
where even the dust is interesting. In the universe.
Speaker 2 (03:55):
Down here on Earth we see dust is sort of
a nuisance, something to brush out of our But out
in space dust plays a very important role in the
formation of stars and planets, and it can reveal that history.
Dust is not just a nuisance. It's a fascinating pile
of tiny clues.
Speaker 1 (04:12):
So today end podcast, we'll be asking the question how
important is cosmic dust? Now? Hopefully this episode won't be
a bust.
Speaker 2 (04:27):
Should we just be sweeping cosmic dust under the cosmic
rug or should we take it seriously and study it
in detail.
Speaker 1 (04:34):
That's a bit of a dusty pun there, you used
it already, But yeah, it's an interesting question here cosmic dust.
I guess it's different than regular dust.
Speaker 2 (04:42):
Well, I think there's fewer dead skin cells and leftover
bits of insects out there floating between the stars than
there is here on Earth. But cosmic dust also falls
to Earth.
Speaker 1 (04:51):
You mean it gets sprinkled from space like powdered sugar.
Speaker 2 (04:54):
Well, you know that space isn't empty, and there's dust
out there between the stars but also between the planets,
and as the Earth moves through these cosmic dust clouds,
it accumulates some of them. Some tons of dust fall
to Earth every year from interplanetary space out there in
the Solar System.
Speaker 1 (05:09):
WHOA is it like dandruff space? Dandruff? Or is that
too embarrassing?
Speaker 2 (05:15):
We had a whole fun episode about where this stuff
comes from. It's a bit of a mystery. There's a
recent experiment though, that tries to pin the blame on Mars.
It might be that dust storms on Mars are blowing
that stuff out into space and the Earth is flying
through Mars's dust clouds. So yeah, I guess it's all
Martian dandruff.
Speaker 1 (05:32):
Yeah, Mars needs some head and shoulders.
Speaker 2 (05:36):
Well first they need heads and shoulders. That'd be pretty
awesome discovery.
Speaker 1 (05:39):
Yeah, or maybe just a hat that might help. But
it is an interesting question. How important is cosmic dust?
Which I guess means Daniel, that cosmic dust is important.
Speaker 2 (05:49):
Cosmic dust is more important than you might think. I mean,
the word dust makes you think it's insignificant. It's just
something to be blown off of. Something else. Man, it
gets in your way, something, it messes things up, something
to be gotten rid of. But dust has clues in it.
This is like the dust here on Earth tells you
who's been living there and the insects that have been around.
Dust out in space tells you what's been happening in
the universe, because there's dust makers and dust consumers, and
(06:11):
dust also plays a big role in making stars and planets.
Speaker 1 (06:15):
Well, you just said dust consumers out in space like
aliens who buy dust. That's what it sounds like.
Speaker 2 (06:22):
Not dust customers. You know, ways in which just is
created and then dust is destroyed. I should say dust destroyers.
Speaker 1 (06:29):
Oh there you go. See that's a device. I would
buy a dust destroyer.
Speaker 2 (06:33):
Wait till you learn how dust is destroyed. You don't
want one of these things?
Speaker 1 (06:38):
Maybe I do. Let's find out. Well, as usual, we
were wondering how many people had thought about the importance
of cosmic does and what role it has in our
search for the meaning of the universe and how it
all works.
Speaker 2 (06:49):
Thanks to everybody who pitches in for this segment of
the podcast. I hear from listeners that they really enjoy
hearing your voices in your thoughts on the episode topic.
If you would like to share your voice and thoughts,
please don't be shy. Write me to Questions at Daniel
Andandjorge dot com.
Speaker 1 (07:05):
So think about for a second, how important do you
think cosmic dust is. Here's what people have to say.
Speaker 2 (07:11):
Stop waving from the universe. I would say that twenty
percent is planet stars, black holes, sixty percent gus, and
the rest twenty percent is dust.
Speaker 3 (07:21):
I think that this is the one of those questions
that but you have to think about some things that
you usually take for granted. So I would say that
the QA is mostly composed by dust.
Speaker 1 (07:36):
All right, interesting, answers here, some people seem to interpret
the questions like how significant is cosmic? Doest?
Speaker 2 (07:45):
Yeah?
Speaker 1 (07:45):
Like, or like how much how much of the universe
is cosmic? Does?
Speaker 2 (07:49):
And they also seem to be taking it as a
leading question, like because I'm asking it, they're figuring probably
it's a big component of the universe and playing an
important role.
Speaker 1 (07:58):
I see, it wouldn't be very interesting just the answer
was just like not at all or nope, nobody cares.
Speaker 2 (08:05):
Yeah, Like how important are Daniel dirty socks?
Speaker 3 (08:08):
Yeah?
Speaker 2 (08:08):
Not interesting, not important? Move on, That wouldn't be a
very fun episode.
Speaker 1 (08:13):
Let's not talk about your socks because I know you
don't wear socks, so.
Speaker 2 (08:17):
Well, then it's a philosophy question, right can my socks
be unimportant if they don't even exist?
Speaker 1 (08:22):
There you go, philosophy of footwear.
Speaker 2 (08:25):
Somebody out there is doing a whole PhD thesis on
that topic, probably.
Speaker 1 (08:29):
On your socks. On socks, and Jackie, I know you're
famous now, Daniel, but geez.
Speaker 2 (08:34):
No on socks? Why they disappear where they go? Why
dryers consume them? See dryers are sock destroyers.
Speaker 1 (08:41):
Nay, it turns them into dust.
Speaker 2 (08:43):
Maybe it transports them to the hozone layer of the atmosphere.
Speaker 1 (08:45):
So let's dig into this topic, Daniel, what is cosmic dust?
Speaker 2 (08:50):
Cosmic dust is an important part of the Solar system,
though it's not a big fraction of the Solar system.
The answer from these listeners made me dig into the
question of like, actually, but is the mass budget of
the Solar system? How much of it is cosmic dust
and how much of it is made of other stuff?
Speaker 1 (09:08):
So what's the breakdown?
Speaker 2 (09:09):
So the Milky Way weighs about one to one and
a half trillion times the mass of the Sun. That's
like our mass unit a solar mass, and the total
Milky Way is about a trillion trillion and a half
solar masses. Now, most of that, like ninety percent of
that is dark matter. We know that the stuff that's
visible in the universe, the stuff that glows, and even
(09:30):
the stuff that doesn't glow that much, like rocks and
dust and asteroids, that's only like ten percent of the
mass of the Milky Way. Out there in the larger universe,
dark matter is a little bit less common than it
is here in the Milky Way. The Milky Way has
more dark matter than an average galaxy.
Speaker 1 (09:44):
And I guess. How do we know these things? Like
how do we know how much the Milky Way weighs?
Do we put it on a scale or something.
Speaker 2 (09:50):
We can measure the component of the Milky Way independently
and then add them up. The stars and the interstellar medium,
the black hole, all that stuff we can measure independently,
and then we can measure the total mass by looking
at how fast the Milky Way is rotating. Because stars
are like tracers, they move around the Milky Way, and
their speed is determined by the gravitational traction of everything
(10:12):
closer to the center than they are. Things further away
from the center on the outer shell don't affect them
at all, things on the inside do. So by reading
the speed of these stars, we can tell how much
mass they're radius encloses, and so that measures the total
mass of the Solar system. And that's how we infer
dark matter, sort of the left over bit that we
can't account for with stars and planets and gas and dust.
Speaker 1 (10:34):
But we can't see all of the Milky Way right
Like we're in the Milky Way, can we really see
the full extent of it and have a good guess
about its composition?
Speaker 2 (10:43):
There's a lot of uncertainty, which is why I said
one to one and a half trillion solar masses. So
that's like an uncertainty of five hundred billion solar masses.
And yeah, part of that comes from the fact that
we can't see the whole Milky Way because we're looking
through it, we're inside of it, and the Milky Way
has a good amount of dust in it, and that
dust obscures our view. So there's a whole region of
(11:03):
the Milky Way that we can't see very well in
many frequencies of light, and that leads to a lot
of this uncertainty. I see.
Speaker 1 (11:09):
So then how much of our Milky Way is dust?
Speaker 2 (11:12):
So it's like ninety percent dark matter, Then it's like
three percent stars, it's like one hundred to two hundred
billion stars. And then leftover is this stuff called the
interstellar medium, which is maybe like half a percent or
one percent of the mass of the Milky Way, and
one percent of that is dust. The interstellar medium is
mostly gas, it's like hydrogen and a little bit of helium.
(11:33):
So one percent of the interstellar medium, which is one
percent of the galaxy, is dust. So the dust is
like point zho one percent or maybe half of that.
It's a tiny fraction of the mass of the Milky Way.
Speaker 1 (11:44):
So I guess you don't count that gas is dust, right.
Speaker 2 (11:47):
That's right. And this is another example of humans putting
categories on things where really there's a smooth spectrum. If
we call it gas, it means it's like a molecule,
there's like h two floating out there, we call that gas.
If it's a larger clump of stuff, a bunch of
molecules together, little grains down like one hundred nanometers or larger,
we call that dust. Get much bigger, we start to
(12:09):
call you like a meteor or an asteroid or even
a planet. But in the end, there's a whole spectrum
all the way down from individual molecules which we call gas,
to larger clumps of stuff which we call dust, all
the way up to much bigger objects stars and planets.
Speaker 1 (12:24):
I guess at some point you get to like pebbles, right,
and little rocks. Is there such a thing as space sand?
Speaker 2 (12:32):
Well, you know this dust is made of carbon and silicates, right,
and sand is mostly silicates. So in the end, like
a lot of this space dust is kind of like
super fine grains of sand.
Speaker 1 (12:43):
But then I also imagine there is sort of sand
sized grains out there in space.
Speaker 2 (12:47):
There are larger pieces for sure, And so this intermedia
category we call dust is not a very big fraction
of the mass of the Milky Way. But to compare,
it's about the same mass as the central black Hole.
Point oh one percent of the Milky Way sounds like
a tiny number. It's a tiny percentage of a huge number, right,
one and a half trillion solar masses. So it comes
(13:07):
out to be about the mass of the central black Hole.
Speaker 1 (13:11):
And so where did all this dust come from? Like
are there giant space aliens shedding of their skin?
Speaker 2 (13:16):
To understand where the dust comes from, we need to
dig into a little bit more about like what is
this dust? And it's made of like a bunch of
different stuff, some tiny little portion of it, this is
really fascinating, comes from the atmospheres of stars. We know
that stars their job is to take hydrogen and helium
and lighter elements and fuse them into heavier elements, although
(13:38):
I have to iron and even heavier in the case
of supernova and in the atmospheres of these stars, especially
when they get really really big and near the end
of their life. Their atmospheres produce these little grains. They're
like coalesce as they cool, and the outflow in the
atmosphere of these stars. That's sort of like one source
of this stuff. But if you look out into the
universe and study this stuff, most of it is not
(14:00):
these presolar grains, these like pristine little blobs made in
the atmospheres of stars. Most of it's been like reprocessed,
like shattered and ground up and reformed into new bits.
Speaker 1 (14:10):
Interesting just from like the churning of space, of stuff
in space.
Speaker 2 (14:13):
Just from the churning of space. It turns out that
you can't just hang out as a grain in the
middle of space. There are processes happening out there. There
are processes that destroy dust and processes that reform it.
The dust destroyers that are out there. It sounds like,
you know, some big alien ship coming along to clean
up the universe, but actually it's shock waves from supernova.
When supernova collapse and then explode, they produce these huge
(14:37):
shock waves, massive amounts of energy, gamma, rays, neutrinos, all
sorts of stuff, and that comes along and it shatters
these grains, destroying the dust and breaking it like back
down into gas.
Speaker 1 (14:48):
Well you know they say space is just a big vacuum,
so those are just suckle. Anyways, So you were saying
that dust is important in the universe. Is it important
to the universe or just to our understanding or to
our search for answers about the universe?
Speaker 2 (15:04):
Well both, Like the history of dust tells us what's
happened out there in the universe. You can take each
individual solar grain if it survived this like interstellar shattering process,
and some of them have, and you can trace it
back to an individual star. Like every star has a
different mixture of elements and a different mixture of isotopes,
so they leave special fingerprints in their solar grains, and
(15:26):
so like ular grain can tell you, like what that
star was. It's like a little sample from that star.
And some of them are made during supernova and capture
elements and isotopes that only exist, we think, in the
atmospheres of supernova during those brief moments that are super
energetic and can tell us about the formation of heavy
elements and what's going on in supernova. So there are
(15:48):
these amazing capsules that tell us about the history of
the universe.
Speaker 1 (15:51):
But I think maybe you don't mean like each individual grain,
do you look? You maybe need like a population or
like a cloud of this dust to sort of know
what the star was like.
Speaker 2 (16:01):
Well, each individual grain tells you something about that star.
Not every grain produced by the star is identical, right,
and the star has a variety of stuff in it,
but each one traces back to an individual star.
Speaker 1 (16:12):
Just each grain would be made out of different things.
Speaker 2 (16:15):
Yeah, each star would make different kinds of grains. There's
going to be some overlap. It's not completely unique, right,
But each star is made out of different kinds of stuff,
different elements, different mixtures. Each star is a slightly different
mass and temperature and so produces different mixtures of stuff
and different isotopes, and so the grains produced by each
star are different.
Speaker 1 (16:33):
Like an individual grain would have different things in it
and different signatures in it.
Speaker 2 (16:38):
Yeah, exactly. The isotopes found in an individual grain tell
you about the star that it came from.
Speaker 1 (16:43):
Mmmm. Interesting, So how is it important to the universe itself?
Because it doesn't seem like it weighs a lot in
the Milca way, So maybe I wonder if it has
a big role in you know, the dynamics of space.
Speaker 2 (16:54):
It does play a big role in the dynamics of
space sort of for two reasons. One is that stuff
heavier than gas is the reason that we have like
planets and stars and stuff like that. Like the Earth
is mostly made out of stuff that's not just hydrogen
and helium, right, and that's cosmic dust gathered together to
form planets. So most of the rocky stuff of the
(17:15):
Solar system came originally from what we would call cosmic dust, right,
those heavier elements that are created by stars and spewed
out into space. And also we think that this cosmic
dust plays a role in the formation of solar systems.
You have a huge gas cloud that eventually collapses into
a bunch of stars. Why does it collapse. It collapses
because it's a little spot here that's denser, that's heavier,
(17:37):
that's cosmic dust. Man, Those are like the iron grains
and the little bits of heavy elements floating around that
seed that gravitational collapse.
Speaker 1 (17:46):
Wait, are you saying the Bible was right? We all
come from dust, from dust to dust.
Speaker 2 (17:50):
And even ashes, right, star ashes.
Speaker 1 (17:53):
Cool And so then how does it help us study
the universe or how does it not help us study
the universe.
Speaker 2 (17:58):
Yeah, it both hurts our ability to study the universe
and helps us. Like it prevents us from seeing things
in the universe because it absorbs light and it blocks
our view. The center of the Milky Way, which is
choked with dust, is famously called by astronomers the zone
of avoidance because they have to look away from that region.
You can't see through the center of the Milky Way
in optical lights, so you can't see what's on the
(18:21):
other side of the galaxy very easily. So it's sort
of a pain for astronomers, but it also captures this
history right, And in order to understand the cycles of
star formation in the universe, we do have to understand
the cosmic dust because the cosmic dust plays a role
in the formation of those stars and is also then
destroyed by the supernovas and then reforms. It's all part
of the cycle of the Milky Way. You might imagine
(18:42):
the Milky Way is just like a bunch of stars
floating in space basically doing nothing, but it's churning and burning.
This stuff going on just sort of much longer time
scales than we're used to thinking about.
Speaker 1 (18:53):
Hmm. Interesting all right, Well, let's get into how we
know where the dust in the universe is and the
very important question where does it all come from? Who's
making this mess in the universe. So let's dig into that,
But first let's take a quick break. All right, we're
(19:20):
talking about cosmic dust, which is not a drug, I imagine,
so it sounds like it might be something you'd sell
on the streets.
Speaker 2 (19:28):
I don't know. If you walk down the street in
Berkeley and you ask people for cosmic dust, I'm pretty
sure they'll sell you something.
Speaker 1 (19:33):
They'll sell you something. But we're talking about the dust's
out there in space between the stars, and it's important
because we're all made out of dust. Stars and planets,
they're all essentially come from dust that gravity pulls together,
and so it's important for that reason. But it also
sort of helps us understand the origins of stars in
the universe.
Speaker 2 (19:54):
Right, even though it's tiny, it's a little bitty part
of the mass budget of the Solar system. It tells
about how things work and it plays a role in
getting those things started.
Speaker 1 (20:03):
But I imagine maybe at some point in the universe's
history dust it was all dust, basically, right, That's where
all those stars came from No, I guess you went
from gas to stars and then those made dust exactly.
Speaker 2 (20:15):
We think that the universe began and dust lists right.
So it's actually an interesting open question in astronomy right now.
It is like when was the first dust made? People
really want to understand the process by which dust is
created and destroyed and helps form new stars, and there's
a lot of open questions out there. We don't really
fully understand the process of it. But we're pretty sure
(20:37):
that the universe began with just hydrogen and helium and
the tiny trace elements of things heavier and no larger
molecules of course, and it's only when stars began to
burn that dust was created.
Speaker 1 (20:49):
But I wonder if in the Big Band, you know,
things were so intense, there was so much pressure, there
was so much violent processes going on, so many of
those that I wonder if some hydrogens aret it e
merging together and make dust without any stars? Is that possible?
Speaker 2 (21:04):
With the earliest dust we've seen is like several hundred
million years after the Big Bang, and it's possible that
hydrogen formed and crystallized somehow earlier on. I don't think
we would call that cosmic dust. Though if it's just
pure hydrogen, probably you just call that hydrogen crystals. I
think to be called dust probably needs to have some
like carbon and some silicon and some heavier elements in it.
Speaker 1 (21:23):
But I mean, could a little bit of a carbon
and silicon have formed in the big during the Big Bang?
Speaker 2 (21:28):
Big Bang nuclear synthesis is a pretty precise science, and
it tells us, based on the temperature and like the
cork density, exactly how much of what was made. And
we think that it's almost overwhelmingly hydrogen, with just tiny
trace elements of helium and then little tiny, anty bitty
bits of heavier stuff carbon. Probably not because carbon requires
(21:49):
the merging of three helium simultaneously. Because lithium is so unstable,
so very unlikely that any carbon was formed, but you
can't say no, it's possible there were tiny, tiny grains
of carbon form during the Big Bang.
Speaker 1 (22:01):
So there could be primordial dust out there, like og dust.
Speaker 2 (22:05):
That's right, The most ancient dust is possible, though the
oldest dust we've ever seen is a few hundred million
years after the Big Bang.
Speaker 1 (22:13):
All right, Well, that brings us to our next question,
which is, how do we know where the dust in
the universe is. It doesn't glow in space, right, It.
Speaker 2 (22:19):
Actually kind of does glow in space, not the way
that stars do. Right. Stars create their own light through fusion.
They light up the whole universe. But everything out there
has a temperature, and everything that has a temperature glows.
Even the Earth glows. Right. It gives off infrared radiation,
and so dust glows in the very very infrared because
dust is pretty cold. So you can see the dust
(22:40):
if you use telescopes that can see infrared light and
so like the Spitzer Space Telescope and a James Web
Space telescope. These things out there can see dust in
our galaxy and in other galaxies by its thermal emissions.
Speaker 1 (22:54):
Like I guess you could tell where there was a
lot of dust and where there isn't a lot of dust.
Speaker 2 (22:57):
Yeah, exactly. You can't see an individual grain. You can
see like huge clouds of dust here and there. You
can see it glowing in the very far infrared. You
can also see dust by how it blocks light. Like
we think we understand how stars glow and the light
that they give off, and dust blocks that light. You know,
it absorbs some frequencies of it, it reflects other frequencies of it,
(23:18):
and so by looking at what astronomers call the extinction curve,
like where's light being blocked, they can measure how much
dust there is between us and something.
Speaker 1 (23:27):
So we measure it by how it much it blocks light,
not how much it reflects light.
Speaker 2 (23:31):
We measure it by how much it blocks light and
also emits a little bit of light in the infrared,
so it depends a lot on the frequency it will reflect.
Blue light mostly infrared light can mostly pass through dust
shorter frequencies where the light has like roughly the wavelength
of the dust that will get reflected or absorbed. So
when light passes through a dust cloud, it basically gets
reddened because the blue light gets reflected and the red
(23:55):
light makes it through.
Speaker 1 (23:57):
It's a little bit of the opposite of what happens
here during the sunset. No, it's the same.
Speaker 2 (24:00):
It's the same. The light gets reddened, right, the atmosphere
tends to reflect blue light, so the sky looks blue
because in direct sunlight it's scattered down to your eye.
That at sunset, the light is coming straight at you
and the blue light is being reflected away and you're
seeing the red light. Mm.
Speaker 1 (24:15):
It filters like it filters out blue light.
Speaker 2 (24:17):
M hmm, exactly, it filters out blue light. And so
when astronomers look out into the sky, they can see
that some stars appear to be dimmed, and they appear
to be dimmed differently across the spectrum. Right, It's not
just like the whole star is dimmer, which might mean
it just further away, but it's dimmed more in the
red than in the blue. So these extinction curves are
really important for astronomers to study because every time they're
(24:39):
looking at something in the universe, they want to know,
like how much dust are we looking through? How much
is dust distorting what we're seeing?
Speaker 1 (24:46):
So technically, does that mean that dust, this space dust
is blue like if you were well, when you sort
of look at it, it's blueish.
Speaker 2 (24:53):
I guess it reflects blue light. It glows in the
far infrared, but it reflects blue light, so I guess
that would make it kind blue.
Speaker 1 (25:00):
Yeah, And have we ever like got in a sample
of dust, Like, have we ever gone out there and
grabbed a you know, vacuum up some dust to study it?
Speaker 2 (25:09):
We do actually have samples of space dust. It's super fascinating.
All the dust that we have sampled is only stuff
in our solar system, so we've never sampled stuff outside
of our solar system. The furthest probes we ever sent
have like just barely left the Solar system. But there's
plenty of space dust here in our solar system, and
many many satellites that we send have little dust collectors.
(25:30):
It's kind of a challenge because these satellites are moving
in very high speeds relative to the dust, so it
can be trickyed like catch the dust. But there are
some missions like the Star Dust Mission, specifically to capture
dust and bring it back, But then lots of other
satellites have like a little space dust collector on it.
We talked once about the JUNO mission that went to
Jupiter in twenty eleven had sort of an accidental star
(25:51):
dust collector on it. The dust was slamming into the
back of the solar panels on the satellite and then
spilating off little bits which you got picked up by
a camera, and it turned out to be like a
huge effective dust collector, and this is how we learned
that Mars is giving off all of this dust, which
is probably responsible for causing the zodiacal light. We have
(26:11):
also captured some dust and broad down to Earth and
studied it under a microscope and seeing like some fractions
of this stuff really are presolar grains, bits of dust
that are older than our solar system. Oh, super old dust,
super old dust. Our solar system is like four and
a half billion years old. But of course stars have
been around for much longer than that, and some of
(26:31):
them died and created these grains, which amazingly survived out
there in space and then formed into asteroids or formed
as part of the Earth, or still just floating out there.
It's incredible that some of these little grains have lasted
so long.
Speaker 1 (26:45):
And we also know how much dust is out there
because it's polarized, right, It's got some sort of electrical charge,
noess to it.
Speaker 2 (26:52):
Yeah, the dust grains are not spherical, right, They have
little shapes. They're irregular, which means that they tend to
be longer in one direction than another. And because they're
made of electromagnetic stuff, sometimes they have an overall charge.
You know. The dust like bumps against itself, it gets
like static electricity essentially, and then interstellar space it will
align with magnetic fields, you know, the Earth has a
(27:13):
magnetic field, the Sun has a magnetic field, the whole
galaxy has magnetic fields. We think there might even be
magnetic fields out there in between superclusters. We talked once
about primordial magnetic fields. Anyway, the dust grains are a
great way to measure those magnetic fields because they align
with the magnetic fields, and then when light passes through them,
it tends to polarize the light because the dust itself
(27:35):
is pointing in a specific direction. So light passing through
this region can tell you about the dust and about
the magnetic fields in that region. It's sort of an amazing
way to like learn about these huge regions of space
which otherwise look empty.
Speaker 1 (27:48):
Well, it's like having special glasses to see the universe.
Speaker 2 (27:51):
Yeah, exactly. So we have lots of ways to study
cosmic dust and to look at the spectrum. And you know,
looking at the spectrum also tells you what's in there,
because if it has like a certain crystal, then that
crystal has rotational and vibrational frequencies and they will absorb
with those frequencies or emitted those frequencies, and so they
can tell what's in cosmic dust. Even if we can't
(28:11):
sample it, like cosmic dust is far far away in
the milky Way. They can tell what it's made out
of based on how it glows and how it absorbs light.
Speaker 1 (28:19):
Hmmm, because that can change, I guess, depending on what
was happening there that made the dust exactly.
Speaker 2 (28:26):
Because cosmic dust is not static, right. One of the
big mysteries is like where's all this cosmic dust come from?
And you know, we think that a lot of it
is made in stars. It's made in supernova, It's made
in these stars called asymptotic giant branch stars. It's made
in super red giant stars to have like just the
right conditions in their atmosphere to coalesce this stuff, like
(28:48):
outflowing and cooling gases will create these grains and shoot
them out into the universe. And that's cool, but it
can't explain all the dust that we see out there.
There's like not enough stars and not enough for of
this dust to explain all the dust that's out there
in the universe. Because, as we said earlier, the dust
doesn't survive forever. Right. The dust is like shattered by supernova.
(29:09):
So we have like stars pumping dust out in the
universe supernova shattering it back in the gas, and that
leaves sort of a mystery because there's not enough being
made by the stars to explain all the stuff that
we see out there, all the dust in the Milky
Way I see.
Speaker 1 (29:21):
So like dust is sort of like they're bigger molecules basically, right,
they're like little tiny pebbles, and inside of the stars
they just burn up I guess, right, because it's so
hot and under so much pressure.
Speaker 2 (29:33):
Yeah, that's why they're made. Like in the outer atmosphere,
the outflowing and cooling gases coalesced into these grains. If
that ever happened inside the star, that would just burn
up as fuel.
Speaker 1 (29:42):
Yeah, like the carbon and all the silicon. It's sort
of gassy within the sun, but once it gets out
of the Sun, it tends to form into molecules and
maybe little clumps mm hmm. But then you're saying like,
once it's out there in space, then if there's a supernova,
the supernova breaks it up back into carbon and silicon exactly.
Speaker 2 (29:59):
So like the typical lifetime for a grain of dust,
it's like one hundred million years. It can float out there,
and then on average it's going to get shattered after
about one hundred million years, some longer, some shorter, but
on average one hundred million years.
Speaker 1 (30:12):
There are that many supernovas happening that to shatter does
so frequently.
Speaker 2 (30:16):
There are not that many supernovas, but they're frequent enough
and powerful enough to shatter this cosmic dust.
Speaker 1 (30:22):
So like on average, for any point in space, you
experience this shattering supernova every hundred million years.
Speaker 2 (30:28):
Yeah, the supernova are more common than every hundred million years.
There's a supernova in our galaxy roughly every fifty years,
so in one hundred million years, you're going to get
two million supernova across the galaxy and they're very very powerful.
So the modeling at least tells astronomers that these things
should be shattered on average within one hundred million years.
Speaker 1 (30:48):
But the Earth has been around longer than that, and
have we experienced such as shattering supernova.
Speaker 2 (30:53):
The Earth has been around much longer than that, but
it would take a very close by supernova to shatter
the Earth. These grains are more delicate than Earth, which
has been like compressed right.
Speaker 1 (31:02):
M So like if there's a bit of dust circling
the Earth, it would get shattered by the supernova, but
not our atmosphere or US.
Speaker 2 (31:09):
Yeah, dust is more fragile. You know, it's floating out
there into space. It's very low pressure. These things are
sort of fragile compared to like a rock on Earth.
Speaker 1 (31:16):
All right, So then the mystery you're saying is like
how it's made?
Speaker 2 (31:20):
Then, Yeah, the mystery is like why is there still
so much of it? There's a lot more cosmic dust
out there than can be explained by this combination of
stars producing it and then supernova's destroying it. There's a
lot more cosmic dust that can be explained by just
that process.
Speaker 1 (31:34):
Maybe the unergy just hasn't bought that neat device you
have to get rid of dust.
Speaker 2 (31:40):
Well, one theory about what's going on is that cosmic
dust itself can reform out there between the stars. So
you take these little pebbles, these little grains, you send
them out there. They get shattered back into gas, but
there's like a tiny little seed left, you know, a
few molecules still cleaning together, and then those can accrete
because they're flowing through these molecular clouds which are super
(32:02):
duper cold, and basically because you have a few tiny,
little grains left, they can like pick up more like
ice can form on these things, and you get these
layers that surround the original tiny core that rebuilds this
thing back up into what you would call dust.
Speaker 1 (32:18):
I see. Yeah, just reforms because and also because of gravity.
I imagine, right, like even if you split a little
grain of dust out there, eventually, gravity is going to
put it back together, isn't it.
Speaker 2 (32:28):
Yeah, exactly? And you know that's the process that eventually
forms stars and planets, right, These little gravitational seeds gathered
together over very long periods, but it begins with gathering
little bits of ice here and there and reforming. And
so some of the cognic dust that's out there are
like og grains that came from their stars and haven't
(32:49):
been shattered, but most of it probably comes from this
process where they have been shattered and then they coalesce,
collecting ice and reforming into grains.
Speaker 1 (32:58):
All right, Well, you mentioned that there are some things
called dust destroyers out there in space and also mysterious
ways that dust is made, and so let's dig deeper
into those things. But first let's take a quick break. Okay,
(33:23):
we're talking about dust and Daniels you're saying, the big
question is where does it come from? Because most of
the dust. If you just put dust out there in space,
within one hundred million years, some distant supernova's shockwave is
gonna shatter that back into its constituent atoms like carbon
and slogan. It doesn't seem that fragile here on Earth, right,
Like if I blow on dust, it doesn't break up
(33:44):
into carbon gas.
Speaker 2 (33:46):
I mean, you're pretty tough, dude, But are you saying
that your breath is as powerful as a supernova?
Speaker 1 (33:50):
Well, some mornings, yeah, But I mean, like it's weird
to think that it's so powerful because here on Earth
we don't feel these supernovas. But you're saying it's drying
enough to like split apart molecules in space.
Speaker 2 (34:02):
The dust is more fragile than the Earth is. Yeah,
and it hasn't been a supernova in our Milky Way
in quite a few hundred years, so it's not like
we're feeling these things every ten years or so. Even
these supernovas are not that common. But yeah, the lifetime
of dust is shorter than the lifetime of the Earth.
So the Earth and planets and stars definitely survived these
super nova shock waves in ways that the stellar dust doesn't.
Speaker 1 (34:25):
So then the mystery is, like, if it is being
destroyed out there in space, why is there still dust?
Why is in and auges gas and individual atoms exactly?
Speaker 2 (34:35):
And it's important that the dust is there because the
dust seeds planetary formation and star formation, you know, in
ways that we didn't always understand. Like back in the seventies,
before we really understood cosmic dust at all, people thought
that our solar system started just from gas, that you
could start from just like a blob of hydrogen and
helium and form all of this stuff, which doesn't really
(34:56):
make sense to me because then like where you're getting
all the iron and all this stuff to make planets.
But now it's very well understood that most of the
iron and most of the heavy metals are bound up
in these cosmic dust grains and you need them to
form solar systems with interesting bits on them like rocks
and people.
Speaker 1 (35:14):
So then are you saying that like just gravity, you know,
pulling all of this stuff out there floating in space
into dust is not enough to account for the dust
we're seeing, Well, why not?
Speaker 2 (35:23):
So just stellar production of dust isn't enough to account
for the dust that we're seeing. You need some way
to reform dust in the interstellar medium, otherwise, as you say,
it would be just gas. But we think that these
little grains probably do gather back together from gravity and
from deecretion of ice crystals. As you pass through a
molecular cloud, there's going to be chemical bonds that form
because these things are a little sticky, right, And so
(35:46):
that is a process that they think might explain where
the gas comes from. I talked to one scientist at
the University of Wasita in Japan who's super interested in
cosmic dust, and she said that this is like the
leading theory for how cosmic dust is being regenerated. But
nobody's like demonstrated this in the lab. They haven't done
tests where they take like a little grain and pass
(36:07):
it through a dust cloud and see this stuff reform.
It's alsort of like theoretical chemistry at this point.
Speaker 1 (36:13):
Well, you need to replicate zero gravity, wouldn't you.
Speaker 2 (36:16):
Yeah, exactly. It's the kind of experiment you'd want to
do out in space or on the iss or something.
Speaker 1 (36:20):
So then that's the best answer to this mystery.
Speaker 2 (36:23):
That's the best answer to this mystery.
Speaker 1 (36:24):
So it sounds like you're saying, like there's a giant
vacuum in space just gathering all this stuff dust.
Speaker 2 (36:31):
Well, you know again it's the supernova, right, Those are
the dust stories shattering it back into gas, and then
they think that it's probably reforming. But another really fascinating
way that they're trying to understand this process is by
trying to answer a related question, which is like how
early did dust form in the universe. So now that
we have like a super powerful infrared telescope, we can
(36:51):
look deeper into the history of the universe and look
for evidence of dust very very early on, like what
is the oldest dust that we can see in the universe,
and they'll give us a sense for these processes because remember,
like stars didn't turn on for a few hundred million years,
so the origin of the dust can really tell us
about like who is making this dust?
Speaker 1 (37:10):
Right I think I mean, like if you look out
into deep space with your telescopes, you're looking back in time,
so like the light you're getting from those deep places
in the universe is really old light, which might be
old dust exactly.
Speaker 2 (37:24):
And we think that most of the dust out there
in the universe right now is probably produced by these
super red giant stars and this asymptotic giant branch stars.
These special stars are super big and have just the
right conditions for this, like outflowing gas to cool and
form these little blobs which then flow down into space.
But the James Web Space Telescope recently saw direct evidence
(37:44):
for really really old grains of stars, like several hundred
million years or up to a billion years after the
Big Bang, too long ago for these stars, Like, we
don't think that there were these super red giant stars
early on in the universe. So probably the first dust
made in the universe were made by supernova from the
first generation of stars.
Speaker 1 (38:06):
WHOA wait, so how do we know we're looking at
dust that old.
Speaker 2 (38:11):
Because we're looking at images of galaxies that are super
duper far away. And so you can look at a
galaxy and you can understand from its red shift how
fast it's moving away from us, and therefore how far
away it is, and therefore the age of the thing
we're looking at.
Speaker 1 (38:24):
Isn't most of that light coming from the stars in
the galaxy.
Speaker 2 (38:27):
Yeah, most of that light does come from the stars,
But we're looking at an infrared telescope, and stars are
much quieter in the infrared, so we're seeing information from
the dust also.
Speaker 1 (38:36):
Oh, I see, like we see the galaxy with a
regular light and then we switch the filter over to infrared,
and then you're basically getting the light from the dust.
Speaker 2 (38:45):
Exactly, and specifically, what they're seeing here is extinction, right.
They're seeing an absorption feature at a very specific wavelength
twenty one seventy five inkstrums that they think is like
a dust wavelength, that that's what dust absorbs. So they
see like a dip in the light in this galaxy
at just the right wavelength that tells them that there
is dust in this very very old galaxy.
Speaker 1 (39:06):
Oh, because I guess the size of your thing affects
what kind of light you're absorbing, right, because you kind
of have to be at about the same size as
the wavelength to absorb it exactly.
Speaker 2 (39:17):
Earlier we were talking about how dust absorbs as various frequencies.
In general, the picture is that it interacts more with
blue light. It reflects that blue light, and it doesn't
interact as much with redor light because, as you say,
it's too small, like the wavelength of light is bigger
than these dust grains so it doesn't interact with them.
But also these things contain specific chemicals and sometimes little crystals,
(39:39):
and those have features that absorb at certain wavelengths, like
little oscillations and vibrational energy levels of these little crystals
inside these dust grains will absorb at specific wavelengths that
are known to be dust wavelengths. So they saw this
in this signature from the James Web Space telescope from
the duper Ancient galaxy, a galaxy too old to whole
(40:00):
any of these red giant stars or ASB stars. So
they think probably this is ancient dust, maybe from the
first round of generation of dust in the universe, probably
from supernova.
Speaker 1 (40:12):
Like the first supernova's right, because that's that's when the
heavier elements are made.
Speaker 2 (40:16):
And it's fascinating because supernova make this stuff and then
also destroy it, so they kind of like clean up
after themselves.
Speaker 1 (40:23):
Right, Wait, how can it make them and destroy them
at the same time.
Speaker 2 (40:25):
These dust grains are made by supernovas sort of in
the last dying minutes of a star's life, where you know,
these shockwaves create really intense environments and specific isotopes, and
then the outflow and the cooling makes these grains, but
then shockwaves from supernova's also destroy dust. Right, supernova are
the dust destroyers of the universe, So they both create
it and they also are responsible for destroying it.
Speaker 1 (40:46):
Which do they do first? Do they first clean up
and then put a bunch of dust there or do
they put a bunch of dust and then immediately destroy it.
Can't be the latter, can it, because then we wouldn't
have any dust.
Speaker 2 (40:55):
It must be that the shockwave from the supernova travels
out faster than dust grains, which means the first they're
cleaning up and then they're making a mess. So I
guess you're right. Actually it's in the wrong order. Or
they're destroying the dust grains from other supernovas and to
make space for their own.
Speaker 1 (41:10):
So they're not cleaning up after themselves. They're just cleaning
it so that they can make a mess.
Speaker 2 (41:15):
Yeah, they're sort of like scrubbing the graffiti off the
wall and then writing their own name on it.
Speaker 1 (41:20):
Yeah.
Speaker 2 (41:23):
I take it back. I take back everything positive I
said about supernovas well.
Speaker 1 (41:26):
They're the reason we're here, so glad they haven't wiped
us off. I guess I'm we're glad that they made us.
All right, Well, what does it all mean about our
understanding of the history of the universe.
Speaker 2 (41:39):
It means that all these processes, the ones that form stars,
that lead to supernovas, that lead to dust creation and
dust destruction, it's all part of this huge cosmic dance.
You know. We tend to think of the Milky Way
as like done, We've made all these stars. They're just
sort of like hanging out and burning now. But it's
a process, you know, and everything is connected as like
dust flowing and swirling. These things are being created, they're
(42:01):
being destroyed, they're being reformed. The whole thing is a big, frothing, active,
lively mess of processes, all of which are important to
creating the universe as we know it.
Speaker 1 (42:10):
Yeah, and it sounds kind of precarious, right, Like basically,
we need a supernova to make all this dust, and
we need the dust to basically clump together into planets
and stars quickly before the next supernova tries to wipe
the board clean. Right, Like if another supernova had gone
off near us, or not even neros, but around us,
(42:31):
before the Sun, you know, got put together and the
Earth got put together, we might not be here. Is
that true?
Speaker 2 (42:37):
It definitely would have affected things, but it's not something
we understand very well. And supernova's contribute in lots of
different ways. Like first of all, they destroy these grains,
but then later on a supernova shockwave can actually precipitate
the gravitational collapse of surviving grains into a new star.
So supernova shockwaves play lots of different complex roles. And
(42:58):
to say like that we even understand this story would
be to overstate it. For sure, there's a lot of
parts of this that we still don't understand. What we
do know is that it's complicated and everything is connected.
Speaker 1 (43:08):
Sounds like our knowledge of it is a little dusty.
Speaker 2 (43:12):
There's definitely a lot of ancient wisdom out there we
haven't yet collected, and we can look forward to blowing
the dust off of all of these.
Speaker 1 (43:18):
Secrets, but not too hard, because then you might destroy
the dust.
Speaker 2 (43:21):
Right, only if you have supernova morning breath.
Speaker 1 (43:24):
All right, I guess the next time you look at
into the nice guy, I know that you're looking at
a bunch of dust as well, not just the beautiful
twinkling stars.
Speaker 2 (43:31):
These tiny but mighty grains play an important role in
the formation of the Solar system, in helping us understand
what's out there, and also in blocking our view of
part of the glorious cosmos.
Speaker 1 (43:43):
Hope you enjoyed that. Thanks for joining us. See you
next time. Hey, it's hoar Hey from the podcast, and
I'm super excited to announce that my new book, Oliver's
Great Big Universe, is available to order now.
Speaker 2 (44:02):
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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