Can Galaxies Exist Without Dark Matter?

We previously thought that all galaxies form with the help of dark matter, but researchers just found a galaxy that doesn't seem to contain any. Learn why that's so weird and what it might mean in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff production of I Heart Radio. Hey
brain Stuff, Lauren vocal bomb here. Dark matter sounds a
little mysterious because it is. It's stuff we can't see
with any existing telescopes, but that math and physics tells
us must exist based on the way that normal matter,
the stuff we can see, behaves, and there's a lot
of dark matter out there. Astrophysicists think that about of

(00:24):
the universe is made up of dark matter compared with
only five percent normal matter, meaning that the term normal
probably isn't the most accurate. Dark matter is the bedrock
that all galaxies are anchored too. You can't get one
without the other, or so we thought, until astronomers found
ghostly galaxy that doesn't appear to contain any dark matter.
It's as if the universe is playing a trick on

(00:45):
us by flipping the laws of physics on their head.
Dark matter should be there, but isn't. It's a game
change your galaxy, astronomers are saying, and it's like nothing
we've ever seen before. We may not be able to
spot dark matter, but astronomers can measure its gravitational effects
acting on normal matter. For example, they can look at
how fast stars cruise around a galaxy. When dark matter
is present, that galaxy's gravity will be bulked up, causing

(01:08):
its stars to move faster than if just normal matter
were present. But in the case of n g C
one oh five two dash DF two, an ultra diffuse
galaxy located sixty five million light years away, astronomers have
found that its stars are moving in exactly the way
that would be predicted if only the total mass of
all the visible stuff is considered. In other words, dark
matter doesn't seem to be exerting its gravity on normal

(01:29):
matter in that galaxy, and that's weird, Peter Van Dulkum
of Yale University said in a statement, finding a galaxy
without dark matter is unexpected because this invisible, mysterious substance
is the most dominant aspect of any galaxy. For decades,
we thought the galaxies start their lives as blobs of
dark matter. After that everything else happens. Gas falls into

(01:50):
the dark matter halo's the gas turns into stars. They
slowly build up. Then you end up with galaxies like
the Milky Way. This galaxy challenges the standard ideas of
how we think galaxies form. Ultra diffuse galaxies are oddities
in their own right, having only been discovered in as
they are very difficult to detect. However, it appears that
this class of galaxy is common, but none are like

(02:12):
the one in question. The galaxy was discovered using the
Dragonfly Telephoto Array, a telescope in New Mexico that's custom
made to seek out these elusive targets. Then, using a
set of twin ten meter optical and infrared telescopes in Hawaii,
the astronomers signaled out ten bright globular clusters, which are large,
compact groups of stars orbiting the galaxy's core. They then
use spectral data to measure their motions. These clusters were

(02:35):
found to be plotting along more slowly than expected, meaning
there's far less mass in that galaxy then would be predicted.
In fact, there's so little mass that the researchers have
come to the astonishing conclusion that there's little, if any
dark matter there. Follow Up observations were made with the
Gemini North Telescope, also in Hawaii, so the galaxy structure
could be studied. With Gemini's help. The researchers ruled out

(02:56):
interactions with other galaxies as being the cause of its
weird dark matter deficit, Ben Docom said in the press release,
if there's any dark matter at all, it's very little.
The stars in the galaxy can account for all of
the mass, and there doesn't seem to be any room
for dark matter. This finding seems to suggest the dark
matter has quote its own separate existence apart from other

(03:16):
components of galaxies. He added, and this makes the very
existence of this galaxy and mystery. If it has no
dark matter, how did even evolve into a galaxy. In
their study published in March in the journal Nature, Ben
Ducom's team speculates that some cataclysmic event in the galaxy
may have cleared out all the dark matter and blasted
away all the star forming gases. Alternatively, a nearby massive

(03:39):
elliptical galaxy may have played a role in the current
galaxies lack of dark matter billions of years ago when
it was undergoing its early and violent stages of evolution. Now,
the researchers are pouring over Hubble space telescopes observations of
similar galaxies to perhaps find more that lack dark matter.
If they find more, then altered, diffuse, and faint galaxies
might be the norm when dark matter isn't press it,

(04:00):
and that's a fascinating development in our understanding of how
galaxies evolve. Ben Docom concluded, every galaxy we do about
before has dark matter, and they all fall in familiar
categories like spiral or elliptical galaxies. But what would you
get if there was no dark matter at all? Maybe
this is what you would get. Today's episode was written

(04:23):
by dr Ian O'Neill and produced by Tyler Clang. Brain
Stuff is a production of iHeart Radio's How Stuff Works.
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