Flares from Infinity: Sagittarius A* Part 1

A super massive black hole broods at the center of our galaxy. In this Stuff to Blow Your Mind two-parter, Robert and Joe discuss just what that means -- and doesn’t mean -- for humanity, our solar system and our future. 

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Episode Transcript

Speaker 1 (00:02):
Further out in the dark, we found alien life. There
were mats of corn colored slime glowing in the deep
as they fed on jets of sulfur bubbling up from
the mud at the bottom of a flooded crater. White
ticks that tunneled through the ice, growing in spindles above
the salt flats, the ruins of empty cities covered in

(00:24):
mosslike growth on quiet planets. But as we journeyed further
in into the hub, into the permanent light, everything was dead.
What could live here? The stars hurtled past one another,
dragging their doomed clouds of matter with them to collide
like weather fronts. The radiation is a hot bath, the

(00:47):
killer surf rocking in from all around. The night swarms
with starlight. But our journey goes on because the Center calls,
We're going to the bottom of the galaxy. Welcome stuff
to Blow your Mind. A production of I Heart Radios

(01:07):
How Stuff Works. Hey you, welcome to Stuff to blow
your Mind. My name is Robert Lamb and I'm Joe McCormick.
In Today we're coming back with some space themed I
was about to say the word content. I'm not going
to say the word content. I'm gonna say space themed stuff.
That's an old favorite how stuff works fans. How about

(01:30):
a space material. There's a lot of discussion of material
and particles this episode in the one that follows it,
because of course we're going to be talking about black
holes once again. Yeah. Now, we did I think a
three part series on black holes. It was sometime last year,
maybe a year and a half ago, but we wanted
to revisit the topic to talk about a specific case

(01:52):
of very interesting black hole that we didn't get deep
into in our last four That's right, So I do
want to just so so really you can go about
this two ways. Uh, you could treat this is part
four and part five. Uh, and you know, go listen
to the three previous black Hole episodes again. But I
don't think it's entirely necessary. I think you can. You

(02:12):
can come in and listen to these is just simply
part one in part two of a look at a
very particular type of black hole, a super massive black hole, right,
and we'll do refreshers on the basics. So it's not
like you've you've got to have done your homework here, right,
you have to have seen either event Horizon or Disney's
The black Hole. Otherwise you have no frame of reference.

(02:32):
That's the starting homework. That's like the summer reading before
you start our podcast in the ball well, you know,
I mean the weird thing is that, you know, those
are two films that I think are in some cases
people's first introduction to the concept of a black hole.
And granted, those are two films that, each in their
own way are loaded with errors and problems and misinformation.

(02:53):
And yet Fantasy black Hole and the Fantasy black Holes.
But you know, a fantasy black hole is I think
a good starting place in many respects. You know, it
gives you a fantastic notion, sometimes an you know, an
action pack very uh you know, terrestrial model of what
a black hole is. And it's not a bad place
to then begin and then build scientifically on the concept.

(03:18):
There is a kernel of truth in the suggestion of
the Fantasy black hole, which is that while we know
more about black holes than we ever have before, and
this year, for the very first time, we think we
got you know, basically a direct image of a black
hole to whatever extent that's possible. And talk more about
the specifics of that later on, But but yeah, while
we still, while we know more than we ever have,

(03:39):
black holes still contain a lot of mysteries. They contain
some edge cases for our theories of physics where what
we know ceases to make sense. And so there's still
a lot of lingering questions, a lot of tantalizing mysteries.
But before we get to the tantalizing mysteries and the
lingering questions, I want to talk about a a nerdy
engineer born in Oklahoma whose middle name is Gooth. I mean,

(04:04):
that's a that's an excellent nerd middle name. Okay, So
I'm going to talk about Carl Gooth Jansky. He was
born in Norman, Oklahoma, in nineteen o five, one of
six children, and his family and Jansky's dad, Cyril, was
an electrical engineering professor. It's a little Carl Jansky. When
he grew up, he followed in his father's trajectory to

(04:25):
study physics and engineering as well. So as a young man,
Karl Jansky earned a degree in physics from the University
of Wisconsin. I think he got his undergraduate degree but
then failed to complete his masters. But then anyway, he
went on to get hired by a company he was
hired for a position as a radio engineer with Bell
Telephone Laboratories in ninety eight, and this would have been

(04:46):
when radio engineering was something fairly new, So at this
time in the late nineteen twenties, Bell Labs was interested
in creating a system for a wireless radio based telephone
service that would allow ins atlantic phone calls and let's
just say you needed to call across the Atlantic Ocean
to order a bagat or something. These radio based phone

(05:08):
calls that Bell Labs wanted to do would have been
in the short wave frequency range, meaning wavelengths of about
ten to twenty meters, and Jansky was given the job
of hunting down any potential sources of radio interference that
would cause static on the calls. So Jansky built a
giant receiver antenna to detect signals at a wavelength of

(05:30):
fourteen point five meters. And this was a directional antenna,
and that meant that it could be moved around to
identify the origin vector of any particular signal. Right, so
it's not receiving signals from every direction the same you
aim it in the direction that you want to pick
up the signal from. And it was mounted on a
giant rotating platform outfitted with motorized wheels. Actually there were

(05:54):
the wheels from a model T and it could be
aimed in any direction to root out the sources of
attic or other interference that they were looking for. Some
people called this Jantski's Merry go Round. I've got a
photo of it here for you, Robert. Yeah, at first glance,
it looks not unlike a giant biplane of some kind,
you know. Oh yeah, with the struts on the wings,

(06:16):
it looks like the world's most dangerous gymnastics equipment. It's
just broken shins all around. Yeah, it looks a little
bit like scaffolding or uh, the system of goals and
some sort of Susian sport. But in the middle, of course,
it's got wheels, and it's got a little track that
the wheels roll around on so that you can aim
it to to calibrate where the source of the interference

(06:39):
is coming from. So, first of all, he discovered the
main source of terrestrial interference on this radio frequency range,
which was electrical storms. So if there's a thunderstorm nearby
that could generate static. You can even get some static
from distant thunderstorms. But Jansky also discovered a source of
noise in this frequency range that seemed unrelated to thunderstorms,

(07:02):
quote a steady hiss type static of unknown origin. This
signal would go through a cycle once a day, peaking
in intensity and then fading roughly every twenty four hours,
but not exactly every twenty four hours, just slightly, just
slightly less than twenty four hours. Now, at first, you know,
what would you conclude if something was emitting radiation powerful

(07:24):
enough to cause terrestrial radio interference in a cycle that
lasted about one day? What would you think it probably was?
But that that brings one's attention to just like the
immediate neighborhood of the Solar system, something to do with
the Earth's position relative to the Sun. Yeah, exactly. You
think it's probably the Sun, right, But Jansky chased the
signal and it turned out it wasn't the Sun because

(07:46):
he kept following it for several months, and while the
signal at some point, I think when he was originally
chasing it was kind of near the Sun, it shifted
over time and moved away. And so after months of
using his radio source finding techniques and teen thirty two
he discovered or I think it was thirty one or
thirty two. He discovered that the origin of this anomalous

(08:06):
static hiss was coming from deep space, and he narrowed
it down to an origin point roughly in the constellation Sagittarius.
Now Sagittarius is named after a a centaur archer. In
Greek mythology, it's associated with the centaur uh An. Ancient
Mesopotamian astrology, the constellation Sagittarius was associated with the deity

(08:31):
near gal a creature of fire and the desert and
war and disease, kind of a a creepy demon type figure.
In Greek and Roman astrology, the constellation was most often
associated with the image of a centaur drawing a bow.
So it's like this super accurate centaur archer who always
hits his mark. Yeah, that centaur's that name is Chion,

(08:54):
mentor of the Greek hero Achilles. Alright, I'd rather like
the idea of of Achilles is the sort of mythical
killing machine having been you know, the student of of
of Well, I don't want to spoil it, but some
sort of cosmic anomaly, like he was getting messages into
his brain from space. Yeah, this was the static kiss

(09:14):
talking to Achilles. Yeah, I mean, well, what is it
to be, you know, to hear the voice of the gods,
but to be, you know, an antenna receiving signals from beyond,
or to get your brain hit by a cosmic ray.
But anyway, like any constellation, Sagittarius, Sagittarius is not a
thing up there. This is something that I often fall

(09:35):
into the trap of thinking of constellations as like objects
that exist in themselves. But of course a constellation is
a number of stars that appear in a certain arrangement
from our perspective here on Earth. It's not like those
stars have a natural association with each other, right, It's
just a yeah, it all has to do with our perspective.
And then it just is a shorthand way of identifying

(09:56):
different different portions of the night sky. They're not objects
in the sky anymore than like the figure of a
shadowy goblin hand cast on your window at night by
a tree limb against the moonlight is an object. It's
feature of your perspective where the lights coming from, where
you're looking from. But an important thing about Sagittarius from
our perspective is that this constellation just happens to be

(10:20):
generally the direction of the center of the Milky Way galaxy,
our galaxy, the one we live in. And this was
what Jansky had discovered, an extraterrestrial radio source coming not
just from space, but from the core of the Milky Way.
Then they get you're prickling a little bit, Yeah, like
something something major is happening there, something that we can detect. Right.

(10:42):
So Jansky authored a handful of scientific papers on this finding,
including a paper called Electrical Disturbances Apparently of Extraterrestrial origin,
which he presented in nineteen thirty three to a conference
in Washington of the International Scientific Radio Union. And this
led to media coverage, including an article in The New
York Times from nineteen thirty three, which you can still

(11:03):
read online if you got a log in with your subscription.
I looked it up and I read it. Can you
guess what the reporters asked to Jansky? Can you just guess? Um?
You probably asked, are their little green men? Of course,
the concluding paragraph of the article is there is no
indication of any kind. Mr Jansky replied to a question
that these galactic radio waves constitute some kind of interstellar signaling,

(11:26):
or that they are the result of some form of
intelligence striving for intragalactic communication. I'm glad they cleared that
up because they specify in the article that was a
steady hiss of random radio static, which seems like a
really bad type of radio signal to use for interstellar
communication would be like trying to communicate with somebody by
handing them blank pieces of paper. Plus ninety three not

(11:50):
a great time period to be visited by some sort
of extraterrestrial civilization. I mean, not that today is you
know that we've necessarily got things in working order, so
that so that some distant civilization can judge us and
decide if we should uh, you know, be left to
function on our own or not. But thirty three was
not a great year, no, not not one of the

(12:12):
best periods. So so he's not saying it's aliens. He's
definitely not saying it's aliens. He's saying it's pretty much
undoubtedly physical, not organic. But what was it? Well? Jansky
wanted to continue research on this deep radio source at
the heart of the Milky Way, but Bell Labs was
of course not interested in funding this kind of thing.
In the nineteen thirties, early nineteen thirties. You know, this

(12:33):
is the depression. They're they're they're not just looking to
to profligately spend money on astronomy. It was enough for
them to have the radio telephone interference issues solved, But
in the following decades many astronomers actually picked up where
Jansky had left off, and Jansky is now remembered as
one of the pioneers of radio astronomy. I've seen it

(12:53):
speculated somewhere that if he hadn't died early he died
pretty young, that he may have received the Nobel Prize
at some point later. But he he hasn't forgotten. In fact,
I almost forgot this. The massive radio telescope array in
New Mexico known as the Very Large Array, which I
visited in person last year and have talked about on
the show before. It's actually named in his honor. It
almost gets forgotten because it's the v l A. But

(13:15):
it's the Carl G. Jansky v l A. Oh okay, cool, Yeah,
I didn't realize that either. And there's also a metric
named after him. And there's a unit in radiophysics known
as the Jansky I can't remember exactly what it is.
It denotes something. But now astronomers have since then has
spent a lot of time and energy trying to understand
what is happening at the galactic center, at the core

(13:37):
of our galaxy. And this is really difficult because we
can't leave our galaxy to look down on it from above. Right.
If you've ever seen an image of the Milky Way
depicted in like a circular shape, this is just a guess,
a guess of an illustrator. We can't look at our
galaxy from outside it. We're in it. It would be
like trying to look at a storm from above while

(13:58):
the storm you're standing on the ground. The storm is
going on all around you. The center of the Milky
Way is especially hard for us to see into because
this region at the center of the galaxy that the
rest of the galaxy orbits around, is shrouded by dust,
these thick clouds of dust that obscure its millions of
stars from our point of view. I've seen numbers that

(14:18):
suggests there are like twenty five magnitudes of optical extinction
from this region due to dust. And that's why, even
though the core of our galaxy is by far the
brightest part of the galaxy, it's lit up with tons
of stars. There's all this dust there that blots out
the light and mutes that brightness from our point of view.
But modern telescopes and equipment have given us other ways

(14:41):
to peer through the dust into the center of the galaxy.
For example, through infrared and other radio frequency detections, we
can see what's shining from within. And today astronomers believe
we have extremely compelling evidence that this radio source at
the center of the galaxy uh Is is a regions
surrounding a gigantic supermassive black hole. This compact radio source

(15:06):
together is known as Sagittarius a star. And if you
see this printed or you know, type, it is a
Sagittarius a asterix. The asterix stands for star, right, Yeah,
it's pronounced star. But it always, for the longest time,
whenever I saw it, it it would confuse me because I'd
see it then it looked like, Okay, I'm looking for

(15:26):
the note and there's not one. Because in astronomy that
that asterix denote star. And we'll get to the you know,
the details on that in a bit. Yeah, it was
named that way for a cheeky reason by an astronomer
in the nineteen seventies. But maybe we should take a
break and then when we come back, we can sort
of do a refresher on black holes and get into

(15:47):
the details of this supermassive black hole. Thank alright, we're back,
all right. So, as we said before, we did a
whole series on black holes about a year and a
half ago. You can go listen to those if you want.
They get way into the history of the discovery of
black holes and all that, but we'll do a brief
refresher here. One quote I really like comes from the
physicist Supermanion Chandra Shekar, who is very important in the

(16:10):
history of black hole research. Uh. And he wrote a
book called The Mathematical Theory of black Holes, and in
the prologue there's a part where he writes, quote, the
black holes of nature are the most perfect macroscopic objects
there are in the universe. The only elements in their
construction are concepts of space and time. And this gets
to some of the history we discussed in those previous episodes,

(16:34):
being that, like, the black hole was the thing that
that we saw in the math before we even began
to like, you know, to to see through uh. You know,
other astronomical means. Yeah, it existed in theory long before
it had ever been detected directly. In fact, you could
only argue probably that that you could well, I don't know.

(16:55):
I guess it depends on what evidence people count. But
there is evidence now that seems to be direct indications
of black holes, but it's hard for reasons that we'll
talk about in a minute, I guess, yeah, for for
the longest black holes. So certainly if you pull out
an older textbook, they're going to refer to black holes
as theoretical objects, right, Yeah, So a black hole is

(17:16):
a region of space time that is so dense that nothing,
not even light, can escape, And this of course means
that you can't see a black hole. There's nothing to
see because the only way we see things is if
they emit or reflect light, and a black hole does neither.
No light comes out of it. If light goes toward it,
it doesn't bounce off and come back in your direction.

(17:38):
It just gets absorbed and never escapes. Yeah, you know this,
this reminds me a lot of how we're recently talking
about casually about quantum mechanics. In a new book that
you've read, about quantum mechanics and and and uh, and
this is kind of that's kind of like the the
micro quest and then the black holes are the macro

(18:00):
quest and the macro into the spectrum. And you know,
both of these are extremes that are just so far
beyond our ability to you know, certainly our evolved ability
to perceive and and to some extent even contemplate, you know,
and and and and so we you know, we talk
about like how we would perceive them vigitally, and even
that is like when you really start turning that over

(18:23):
in your head, um, it's it just gets ridiculous really quickly,
you know. Well, it forces you to think about the
nature of physical information. Yeah, the fact that you know,
a black hole highlights the fact that when you see
a thing, you never really see the thing. You're seeing
light reflecting off of it, which is, you know, that's
our most common way of sampling the world. So it

(18:43):
makes sense to just think about that as a short cut. Yes,
when I see the light bouncing off of a coffee cup,
I see the coffee cup, but you're not, you know,
you don't have the coffee cup within you from that,
it's just light. Yeah, with our site, with with certainly
healthy human side. We kind of have this illusion that

(19:04):
that we that we are cited, that we can perceive.
But the more we look at things like the microscopic world,
in the macroscopic world, the inner space and and outer space,
you really begin to feel that we are not cited
at all. We are just so incredibly blind. And the
only way that we are really really have been able

(19:25):
to understand h nature has been through scientific inquiry that
I guess you could you could relate to the like
the blind pawing of of the blind men and the elephant,
you know. Yeah, And astronomy is a great way to
highlight that. Astronomy and well you pointed to both ends
of the scale, you know, physical scale, the quantum mechanics

(19:46):
world and astronomy what's out there in the dark beyond Earth.
They both really highlight ways in which the universe is
full of hugely powerful, consequential phenomena that we not only
don't regularly see, but we can't even understand when we
when we detect it with other means right and in

(20:06):
both totally violates our intuitions and in both directions, both
towards the small and the large. You know, we can
optically enhance the telescope or the microscope, but in both
directions there reaches a point where optical enhancement uh doesn't
get you anywhere, and we have to rely on other
means of of pawing at the uh you know, at

(20:28):
the the the the the Titanic forces on an either
end of the spectrum. And that's something that, of course,
we get to with Jansky's discovery, right, this idea that
there are these powerful sources of information coming into the Earth,
but it's not information that anybody would be able to
see with their eyes coming in radio frequencies and then uh,
you know, other frequencies of light. But I guess to

(20:49):
get back to black holes, we should ask the question,
of course, how is it possible for an object to
be so dense that it neither reflects nor amidst light?
Like what what happens to the light when it goes in?
Why that be the case? Uh? So, the basic principle
is the greater the mass of an object, the more
difficult it is for an object that is moving away

(21:10):
from it to escape its gravity. Well, now, all sources
of gravity have their own particular escape velocity and If
I'm standing on the surface of the Earth and I
throw a cantalope straight up in the air at a
hundred kilometers an hour, it's of course going to fall
back down to the ground. If I throw the cantle
ope at two hundred kilometers per hour, it's going to
go up farther, but of course it will eventually slow down,

(21:31):
reverse course and fall back to the Earth. But if
I keep throwing it up in the air greater and
greater velocities each time, eventually you will reach some velocity
where the cantalope doesn't fall straight back down to the ground,
but it goes up and up and up, and it
breaks free of Earth's gravity, and then it just keeps
on flying out into space. It maintains its momentum and
goes in the other direction. Now at the surface of

(21:53):
the Earth, this velocity for objects that don't keep propelling
themselves as they travel, is about eleven point twokilometers per second,
so it's very fast. Humans have never made a terrestrial
vehicle that goes even close to this fast with humans
in it. Certainly, our our launch vehicles that put things
into orbit or send them into outer space don't go

(22:15):
that fast. At first. Heavy launch vehicles like the you know,
Saturn five rocket and things of that ilk are able
to put things into orbit or beyond by applying continuous
thrust as they achieve higher and higher altitude. So the
rocket keeps on pushing and pushing by ejecting more exhaust
until it gets up through the atmosphere. And then, of course,
inside the atmosphere, air resistance and frictional heating would be

(22:38):
a huge issue if you try to have a spacecraft
achieve escape velocity too early, right, your spacecraft would probably
get too hot and burn up. But once outside the atmosphere,
rocket can keep accelerating. In the vehicle can get up
to the ultimate speed that it needs to go into
orbit or leave Earth's gravity overall, and it turns out

(22:59):
this escape velocity logic even applies to light. At a
certain point, an object becomes so dense, there's so much
mass inside such a small space that the escape velocity
for an object exceeds the speed of light. So no
light comes out of the black hole, No light is
emitted from within, no light is reflected from without. It's
a perfect vortex. It swallows everything that comes within a

(23:23):
certain radius, and of course if this applies to light,
it doesn't just apply to light, right, because since nothing
with mass can travel faster than the speed of light,
speed of light could also be thought of as a
kind of speed of information or a speed of causality
in the universe. If light can't escape the black hole,
nothing can escape. Now. Something I think a couple of
listeners were asking about after our last black Hole series

(23:46):
was trying better to picture exactly what's going on there, Like,
what is it that nothing can escape? In some ways?
Could a black hole be kind of like a solid
black bowl, like a black ball that you get stuck
to the outside of like paper, you just get flattened
against it. I think the answer to that is no.
A black hole is matter that has collapsed on itself

(24:08):
to what looks to us, at least through the math,
like a point of zero volume and infinite density, and
this is sometimes called the singularity. Now, is it actually
physically possible to have a point of infinite density that
may be not something that we're supposed to literally picture.
Is what's there? But an indication that we don't have

(24:29):
a correct theory of quantum gravity yet, and you know,
we just don't understand exactly what's happening there. That's where
general relativity breaks down. But I think what it does
make sense to say is that there is some kind
of point of extremely tiny collapse at the core of
the black hole too. That doesn't really make any kind
of intuitive sense to the physics, you know, engine in

(24:49):
our brains. And then of course there is that that
that point of no return as well. That plays into
our very perception of the black hole, right that point
of no return and is often what we think of
as the black hole. But that's not necessarily stuff. That
is a region of space around this point where all
the all the original matter that made up the thing

(25:11):
that became the black hole is collapsing into. So that
is the event horizon. Yes, exactly, it's the sphere shaped
region of space that's a kind of gravitational exclusion zone.
The size of this zone, of course, depends on the
mass of the black hole core. So a more massive
black hole will black out a larger region of space
in the sphere around it. I think we uses we

(25:33):
might have used this very um analogy before. But if
if the black hole is the killer inside the haunted house,
the event horizon is the haunted house. Okay, So like, uh,
you know, you can say that the black hole is
leather Face, but the event horizon is the leather Face

(25:55):
family home. Can you see people walking towards and never
emerging from. Oh, but Marilyn Burns does escape, Well, I'm
talking about earlier the film. You're okay, Okay, Obviously, I'm sorry.
I didn't mean to nitpick your analogy. Obviously, obviously people
have to escape the film. I have to escape the
house for a proper horror movie to work. But in
a version of the leather Face movie where nobody ever

(26:16):
comes out, then like that is the event arison. Perhaps
there's there's a there's a more fitting example from from
like haunted House lore out there. I guess it would
make the story is less interesting if you just know
that nobody ever escaped. I think Stephen King had a
short story about a women's bathroom that functioned like this,

(26:37):
where like people went in but they didn't come out,
and and like the the the point of view character
was just trying to figure out what was happening. I
only have a vague memory of this. I think it
was like a real shorty, or maybe it was just
him talking about a concept he had that he had
not written, King Fans will have to straighten me out. Then, well,
we're we're like that person outside the bathroom trying to

(26:59):
figure about what's going on because we can't look inside
and see. Uh So, the edge of this region of space,
of course, as you said, is one name for it
is the event horizon. But the distance between the core
of the you know, what's known as the singularity, the
core of the black hole, what everything, the point that
everything collapses down into and this event horizon is known

(27:20):
as the schwartz Shield radius, named after the twentieth century
German astronomer and physicist Carl schwartz Shield, who did very
important calculations in the early days of black hole theory,
back when black hole theory was still ridiculed as being
something that, you know, couldn't possibly be found in nature.
I think it was that Arthur Eddington who originally said, uh,
you know, when when Chandra Sheker and the others were

(27:42):
proposing the idea of black holes, Eddington was like, surely
nature would forbid such a preposterous event. That's one of
those great times when nature faced a scientist who thought
nature couldn't be that weird, and of course it is
always the case. Nature is far weirder than can possibly imagine,
of course. But yeah, anyways, this sphere of space from

(28:04):
which nothing returns. Anything that passes within the short shield
radius enters this strange world of warped space. And from
this space it is impossible to escape. Once inside the
event horizon the short shield radius, there's only one direction.
That direction is down. No matter what you do, you're
headed towards the center of the black hole. And I

(28:24):
should add quickly there may be exceptions to these rules
for special types of black holes with exotic properties. You
find articles about these, like weird types of black holes
where things can change. But this is the basic I
think you're non rotating standard stellar blast. Yeah, this is
your standard model. Now, we alluded to earlier the fact
that even though a black hole neither emits nor reflects light,

(28:48):
we do have pretty solid evidence now that black holes
do exist. Uh, They're not just something that is sort
of hypothesized by the theory of general relativity. But like
we we've we're pretty certain we've detected them out there
in the universe. Now, so how can you detect them
if they neither reflect nor a mint light. Well, I mean,
it's kind of like the hunted house scenario, Like if

(29:10):
there was a house like this that no one ever
emerged from again, because there's some sort of uh, you know,
diabolical force within it that consumes everyone that passes within
a you know, past its threshold. Obviously, you could note
people that entered the house and didn't come back out again.
You might notice the um the effect that such a
house would have on the the surrounding property values, um

(29:34):
you might have. You know, basically, it would have some
effect on the surrounding environment that would be observable even
if you never got to actually pass within its walls
and see the dark, hideous force that is murdering people. Yeah,
I think that's exactly right. You can observe a black
hole by looking at its effects on surrounding objects. And

(29:54):
one of those types of effects is gravitational effects. Imagine
you see a dis stant star orbiting some invisible point,
and that star's orbit is it's it's on a very
irregular trajectory, maybe a super stretched out ellipse, and at
one end of that ellipse, it appears to be going
really close to the thing it's orbiting. Around but that

(30:16):
we can't see, and as it goes really close to
that thing, it accelerates to unbelievable speeds. There would be
a good case to be made that maybe what it's
orbiting is something that is incredibly tiny and incredibly massive,
And in fact, this is exactly what we see. Especially
with the case of Sagittary as a star the hypothetical

(30:37):
supermassive black hole at the center of our galaxy that
we were alluding to earlier, we have noted the passive
the transit of stars around it that suggests that the
thing these stars are orbiting could only be a black hole,
because otherwise there's nothing else that could be as small
as the thing they're orbiting and accelerating them as fast. Now,

(30:58):
another way you could look at the surroundings of an
object and determined that it's a black hole is if
stuff is basically stuff is catching on fire, not on fire,
but it's getting really hot. Um as matter like gas
and dust, swirls around a black hole and eventually falls
over its sword shield radius. In this process of swirling
around and falling in, it gets accelerated to incredible speeds

(31:22):
and superheated, blasting out hot radiation that that is some
of the brightest stuff we can see in the entire universe,
like this idea of quasars, these you know, quasi stellar
radio radio emitting objects out there in the universe. We
tend to think that what these things are are the
cores of galaxies that have supermassive black holes at the

(31:44):
center of the galaxy. And as stuff is falling into
the supermassive black hole, it gets accelerated to such a
way that to such an extent that it becomes unbelievably
bright on the on the electromagnetic spectrum. So again for analogy,
you can you can think of this like imagine there
were an invisible blow torch floating around in a forest.

(32:06):
Like you couldn't see the blowtorch, but you could notice
that all the leaves in the wind swirling around a
certain area of space or all catching on fire for
some reason. And then another thing, of course, is that
data collected from gravitational wave of observatories has picked up
waves propagating through the universe that seem to be best
described by the collision of black holes. Now we know

(32:27):
there are a few different kinds of black holes, right,
so we know that there, there's your standard model stellar
black hole, and these are created by the collapse of
large mature stars. Our Sun is not massive enough to
become a black hole. Uh. In something like four to
five billion years. Our Son's probably like halfway through its
its main sequence life. In about four or five billion years,

(32:50):
it's going to swell up into a red giant that
will absorb the orbits of mercury and venus and possibly Earth,
and then it will go through a series of different
internal chemistry phases, is where it's fusing heavier and heavier
elements as it runs out of its lighter fuel, so
it'll run out of hydrogen, then fuse helium, run out
of helium, and fuse heavier and heavier elements uh. And

(33:11):
then eventually it will end up as a white dwarf,
which is what it will remain for trillions of years
basically until it just cools off. It's interesting, we keep
coming and we'll keep coming back to the the idea
of between four and five billion years old, like and
again stressing that the Earth is what four point five
billion about years old, So in a few via the

(33:32):
a few different calculations, like the Earth is half done, Yeah,
assuming nothing else happened to it before then. Yeah, uh though, yeah,
I think the the habitability window for the Earth might
be a bit shorter than that, yes, because things might
get worse before before the Earth is actually even potentially
swallowed up right, And then of course the's a whole

(33:53):
there's an additional discussion about, you know, do we reach
a civilization level at that point where we have the
technology to do something about it, say, move the Earth, etcetera.
But that's another podcast unto itself. Yeah, the scoutow thruster
or whatever. Oh no, wait, no, that brings the star
with us. We don't want that, need better star. But anyway, Yeah,
so the Sun is not large enough to become a

(34:15):
black hole. If our Sun were a lot larger, maybe
about ten times its current mass, you could expect that
when it exhausts its hydrogen fuel and begins fusing heavier
and heavier elements, it could eventually end up trying to
fuse a dense core made of iron, which is the
chemical death ritual of a star fusing iron. Is that's like,

(34:36):
that's like the character in the horror movie saying, is
anybody there? That's just you know, there's no returning After that,
fusing iron leads to not enough outward pressure to hold
the mass of the star up against its own gravity,
and it collapses inward catastrophically. It releases a giant blast
of energy and eventually perhaps turns into a super dense

(34:57):
neutron star or even a black hole. But again this
depends on the density of the thing that's left there
after this event. If our son had the same mass
it does now, but it was only a few kilometers wide,
supposedly it would collapse into a black hole. There's just
no reason to think that it would ever be that small.
But there are other kinds of black holes that we
can't say are formed necessarily from the collapse of large

(35:20):
stars after they exhaust their fuel supply of lighter elements.
There is, for example, a hypothetical type of black hole
called the primordial black hole, which if they did exist,
would have formed due to the gravitational collapse around dense
regions in the very earliest periods of the expanding universe.
And then there's this other class of black hole, the
one that Sagittarius a star would be if if there

(35:42):
is in fact a black hole there, and we think
there's very good evidence there is, uh, these remain more
of a mystery to us. This is the These are
the black holes found at the cores of massive galaxies. Yes,
some of the theories that we have for the formation
of sort of the standard black holes, they don't quite
hold up when we try to use them to explain

(36:03):
a supermassive black hole, like they either like one example
is looking at was that they don't they don't create
these simulations do not create a supermassive black hole fast enough,
you know, for them to be present in the universe. Yeah,
that's right. There are competing hypotheses to explain the formation
of supermassive black holes. But it seems like, at least

(36:23):
as far as I've read, there are problems with all
of the proposed hypotheses. I was reading one article that
can consults a scientist and Mitch Bagelman of the University
of Colorado, who works on supermassive black hole formation and
and basically he was saying that the theories fall into
two main categories. One is that you've got an original

(36:44):
small seed black hole that takes a long time to
get bigger as it absorbs more and more material, or
you've got a very large original seed black hole from
the collapse of some kind of hypothetical huge star that
we're you know, we don't usually see, and it rose
very quickly. But there are problems with both of these
classes of explanations. But then there there are other more

(37:08):
I don't know, more exotic theories as well. I guess yeah.
When I was looking at is from seen from the
Cavali Institute for the Physics and Mathematics of the Universe
UM principal investigator uh nail Key Yoshida at All produced
a paper in Science on this with an interesting take,
uh you know, a different a different proposition for how

(37:29):
a supermassive black hole might form against something something different
from just the idea that it's the first generation of
stars that have turned into black holes, and something different
from just the idea that, you know, a massive primordial
gas cloud that collapses under gravity. So this is how
they lay out an alternate formation. First of all, you

(37:50):
have a massive clump of dark matter, which forms when
the universe is just a hundred million years old. Then
supersonic gas streams generated by the big dayg are caught
by it and form a dense gas cloud, a protostar
forms inside um of this gas u and a protostar
is a young star that is formed by gas cloud collapse.

(38:13):
And then this protostar feeds on the gas cloud around
it and grows at an accelerated rate. And then the
protostar grows to a mass of thirty four thousand times
that of our Sun. And all this by the ways
in simulations they were running, uh, and then it collapses
in on its own gravity, birthing a massive black hole
in the early universe that only grows more massive and

(38:36):
more gravitationally dominant as time grinds on. And this would
explain why all or most massive galaxies appear to have
a supermassive black hole at the center of them. Yes,
that though, that is what they're trying to explain with this.
But again, this is just another hypothesis for how what
could have occurred to bring these things into being. Step

(38:58):
one assumed dark matter. It makes sense to be uh
looking at all different kinds of simulations because because I
mean that again comes back to the origin of our
understanding of the black hole. It began as this this uh,
this vacancy yeah, in the in in the mathematics of
the universe. Yeah, well, yeah, it began as a simulation.
It was like these people running these different hypothetical simulations,

(39:20):
but then it turned out that they actually exist. So
maybe we should take a break, and then when we
come back, we can look at some specific facts about
this compact radio source at the center of the Milky
Way galaxy, about Sagittarius A Stark. Alright, we're back. We're
talking about supermassive black holes. Uh, not the Muse song,

(39:42):
though I ended up being reminded of the Muse song
Supermassive black Hole and and listen to it at least
once during a research for this. If I know that,
oh yeah, it's it's pretty good. Yeah, news has some
great tracks, but hasn't been I don't think they're you know,
astrophys sally accurate per se, but never mind, but I

(40:04):
guess they're more accurate than say, you know, Sam Garden's
black Hole Sun, which again, uh, as we already covered,
is not actually going to happen no matter how many
times we watched that music video. Growing up what was
a long time ago, when we were doing how stuff
works articles, I remember us brainstorming a like false science
facts in song lyrics. Uh, and I remember that that

(40:27):
was the one that came up. But another one that
I'm made a case for and I don't think made
it into the article was Fleetwood Mac thunder only happens
when it rains. Not true, Not true at all. Yeah. Yeah,
it's still a great track though. Yeah, they can't beat
the Mac. Alright, Well, let's talk a little bit more
about Sagittarius a star. Um So, I just want to

(40:50):
just take apart its name a little bit more of
which I think helps us understand exactly what we're talking about.
Uh So, first of all, we've been talking about it
being not only massive but super massive, Like what does
that mean? Well, we're talking about roughly four point one
million solar masses, with one solar mass being equal to
the mass of our own son. So a single solar

(41:11):
mass is two times ten to the thirty power kilograms
are roughly two quintillion kilograms. The mass of of Sagittarius
a star is roughly four point one million times that
of our son. I was trying to find a point
of comparison, so I was doing a little math, and

(41:33):
one worked out just right. I think it's roughly the
difference in mass between a twenty milligram house fly and
a one hundred and eighty pounds Gean Claude van dam
our Son is the fly twenty milligrams. Van dam is
the supermassive black hole at at a hundred and eighty pounds.
That works out just about right. All right, So we're
talking like um, like time cop era vandam right. I

(41:55):
mean here, I don't know. I just googled hundred vander
because he's pretty dense, right, I mean it would be
a good analogy for a black hole, I guess. So, yeah,
that's right. Yeah. What's the thing he does in time
coop to kill somebody? Oh? He does all sorts of
things to kill somebody. I mean he he does the
splits on on some kitchen sinks so that somebody electrocutes himself. Uh.

(42:17):
He somebody is frozen with liquid nitrogen, and then he
kicks their arm off. Um. I mean things get super
trippy when he takes ron silver of the past and
Ron silver of the future and kicks one into the other,
and then they merge into a cosmic Google. Oh, there's
got to be a black hole analogy there, right, black
hole takes past you in future you and merges you somehow. Yeah,

(42:39):
I've never quite worked out the science of that scene,
but it has always stuck with me. Perhaps a reviewing
of time cop Is is worthwhile in the future. Okay,
but yeah, so our Sun is much bigger than the Earth,
and the Sun is a housefly compared to his John
club van Dam with the supermassive black hole. As we know,
because of the limit physics that rule them, black holes

(43:01):
don't quite take up the same amount of space as
normal objects of the same mass. So how big is it? Well, yeah, well,
let's let's talk about it's radius. Roughly it has it's
roughly thirty one point six solar radius, So that means
it's radius is thirty one point six times that of
the radius of our own son, which is, by the way,

(43:22):
six hundred and ninety five thousand, seven hundred kilometers or
roughly four three hundred miles. Remember that the radius is
half of the diameter. So even though it's more than
four million times the mass of the Sun, because it's
a black hole, it's still not like so wide that
it would swallow up the entire Solar system if it

(43:43):
were in the Sun's position, right, Just talking about like
the physical space, it takes up its circumference. The distance
around it is roughly forty four million kilometers or twenty
seven roughly twenty seven million, three hundred forty thousand, three
hundred and thirty two and a half miles and a half.
Now this is really big, But it got me wondering.

(44:03):
Is Sagittarius ay started the largest black hole we know about? Nope,
not even holose. Contemplating the biggest ones should make your
head implode if it hasn't already. How much bigger can
black holes get? Well, it's hard to be certain because
the mass of the black hole at the center of
another galaxy has to be inferred right based on these
periphery clues, like the brightness of the emissions presumed to

(44:25):
be from its accretion jets or accretion disk or relativistic jets.
Uh So, we don't know for sure, but we have estimates.
Just one example on the highest end of estimates is
a black hole called Town six eighteen t O N
six eighteen and unbelievably luminous quays are and a galaxy
billions of light years away. One of the brightest objects

(44:48):
in the universe, the presumed supermassive black hole at the
center of this radio source has been estimated to contain
sixty six billion solar masses, and so it's thought that
the the brightness of the stuff swirling into that supermassive
black hole, it just completely outshines everything around, outshines all

(45:08):
the stars in the galaxy around it. So sixty six
billion solar masses with with the tonight compared to Sagittarius
a star, which again four point one million solar masses, right,
that's incredible. I mean, we're going from like unimaginably huge
to um to something even beyond that. It's like four

(45:30):
orders of magnitude above. But going back to Sagittarius a star.
How close are we to it? Yeah, I have some
people may be wondering that we're roughly twenty five thousand,
nine hundred light years away, give or take one thousand,
four hundred light years. This is going to depend on
orbital positioning. Okay, so this is the very center of

(45:53):
the Milky Way galaxy, and we're sort of in the middle.
We're sort of like halfway out right between the center
of the galaxy and and the farthest reaches of its arms.
Very roughly, we're basically in a stable orbit around it. Yeah, because,
as we'll discuss the I would think probably more in
the next episode. Things get really rough the closer than
you get, which should not come as a surprise. Uh. Now,

(46:17):
we've already talked about the name itself, Sagittarius, the ninth
astrological sign associated with the constellation Sagittarius, it's connection to centaurs.
But let's come back around to that A star business.
Oh yeah, so this is this thing can be confusing
to a lot of people. We mentioned that it often
makes us look for a footnote at the bottom of
the page. I was looking into where the A star

(46:39):
part comes from the asterisk, and I found a two
thousand three paper by Goss, Brown and Low that explains
the origins. So astronomer Robert L. Brown and colleague Bruce
Ballack are credited with discovering the compact radio source of
Sagittarius a star in nineteen seventy four, and Brown apparently
named this object according to a made up convention that's

(47:01):
kind of nerd cheeky. So he writes, quote, scratching on
a yellow pad one morning, I tried a lot of
possible names when I began thinking of the radio sources
the exciting source for the cluster of HII regions seen
in the v l A maps. The name Sagittarius a
star occurred to me by analogy brought to mind by
my PhD dissertation, which is in atomic physics, and where

(47:25):
the nomenclature for excited state atoms is H E star
or f E star, meaning like you know, helium star
or iron star. So the star there is the excited
state of the atom. And apparently this discovery was exciting
in more ways than one. Now, one of the other
reasons it is can it can potentially be confusing is
because asterix means star. I mean, it basically derives from

(47:48):
the Greek aster riscos, which means little star um and
and another thing to keep in mind, I guess is
that you know it's we're basically dealing with an astronomical
radio source is the likely location of a supermassive black hole.
Uh So, I guess it's more like referring to an
unknown serial murder as the Green River Killer before you

(48:10):
ever find out that his name is actually Gary. And again,
as as you pointed out, it's also kind of like
cheeky and uh and I think I've seen it referred
to as being historical in nature, but there's also a
broader thing of just Sagittarius A without the star. The
star is this compact radio source believed to be the
location of the supermassive black hole or the let's see

(48:31):
the radio source emitting stuff around the supermassive black hole. Yeah,
and then there's there's more two because there's a there's
a Sagittarius A star, but there's also Sagittarius A east.
This is likely the remains of a supernova explosion that
occurred between thirty five thousand and a hundred thousand b
c E, and scientists think that the ejecta of the

(48:52):
supernova was gravitationally compressed due to a close approach by
the supermassive black hole. Then there's Sagittarius A. Well, this
is the mini spiral. It's sometimes called because from our
perspective it looks like a three armed spiral, but it's
actually a cloud of dust and gas. It's orbiting Sagittarius
A star. And another question people might have was how

(49:13):
old is Sagittarius A star? How long has there been
a supermassive black hole festering at the center of our galaxy. Well,
the answer I guess is it's it's staggeringly old. But
it's hard to put a real fine line on that.
The Milky Way galaxy itself is what the thirteen point
two billion years old, and there are different formation theories

(49:38):
regarding galaxies, and the universe itself is believed to be
roughly thirteen point seven thirteen point eight billion years old.
So um, yeah, I'm I think we can stand by
staggeringly old and is it the center of things? You know,
for for a reason? Yeah, And now when we think
about that compared to say, our own solar system, our

(49:59):
Solar system is just roughly four and a half billion
years old, and it's one of the reminders that our
Solar system and everything that makes our planet possible, that
makes our bodies possible, it's not the first generation, right.
We can only exist by the fact that previous generations
of stars lived and burned and died catastrophically, creating the

(50:21):
heavy elements that make up things like the planets in
our Solar system. All the technology you're using to listen
to this right now, and all the stuff in your
bodies that's all made of gunk from Stars that went
horribly wrong. Now, I think one important thing to keep
in mind, you know, whenever we discussed black holes, but
especially in this episode as well, is that despite the

(50:43):
black hole being you know, a source of peril in
various science fiction treatments, despite the fact that even in
this episode we've we've discussed it and often like dark
and forbidding ways, you know, it's not coming to get you. Yeah,
it's not coming to to get us in. But then
even more to the point, it is, um it is
not like this negative like counterpoint. You know, it's not

(51:07):
this evil thing in the universe, like the black The
idea that there's a supermassive black hole at the center
of our galaxy should not come as uh, you know,
a point of fear or disappointment. You know, it's not.
It's wonder and it is. It just shows that the
black hole can be a thing that holds, uh holds

(51:27):
everything together. You know, these are that's part of the
building blocks of of of the galaxy of the universe.
And uh, you know, therefore we we can't think in
you know, simplistic terms about it being you know, just
like some sort of venomous uh you know, has us
off like formation. No, it's not venomous, because what the

(51:47):
venomous thing would would inject you with venom? Right, this
sucks it out? Yeah yeah, I mean if anything is
injecting us with venom, right, it's the solar radiation emerging
from a start that necessary to life. To be fair,
I guess the supermassive black hole what it Emits lots
of radiation, so you can think of that is it? Anyway,
It's not venom It's just a fantastically interesting object out

(52:11):
there in space, so much so that we want to
do a whole other episode on it. We we wanted
to come back next time and deal with everything you've
always wanted to know about the supermassive black hole at
the center of the galaxy. But we're afraid to ask, Yeah,
can you live on it? Um? Can you eat it?
Questions like this? You know we will. We will get
into in our next episode. In the meantime, if you

(52:31):
want to check out other episodes of Stuff to Blow
your Mind, you know where to find them. Stuff to
Blow your Mind dot com. That's where you'll find them all,
including those previous episodes on black holes. Likewise, we mentioned
Invention If you go to invention pot dot com you'll
find our other podcast, Invention. That's where you'll find that, uh,
that episode on the telescope that came out, as well

(52:51):
as episodes on the you know, the the the invention
of the photograph, the motion picture, etcetera. It is a
invention by invention, an exploration of human techno history and
let's see what else. Yeah, If you want to support
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(53:13):
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(53:42):
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