>>MORDECAI-MARK MAC LOW: My name is Mordecai-Mark Mac Low
and my position is Curator of Astrophysics.
Dark matter was
first identified and even named by a character named Fritz Zwicky
who worked at Caltech— famous not only
for his excellent astronomy, but also for his
scatalogical language. He would rarely say anything that could be
quoted in polite company. Nevertheless,
he made several extremely important
discoveries,
one of which was that if you look at
galaxies
in clusters, they orbit around each
other.
From the speed of the orbit, you can measure the mass of the cluster.
So, that's what Zwicky did. So, he adds up the mass of all the galaxies
in the cluster and compares it to
the mass that he's derived from the velocities. And
it's not even close. So,
he says, "There must be some sort of
dark
material—dark not emitting light, like the stars are—
that is making up all this missing mass.
When this was first published,
everybody said, "Okay we don't really understand
galaxies in distant clusters anyway," and
the result was
largely ignored for 40 years. Vera Rubin and
her collaborators in the 1970s found
that even if you look at individual
galaxies, they still move too fast.
And that was even harder to explain and
brought people's attention back to this old
question of why do galaxies in clusters move so fast?
What we know now about dark matter
is that it isn't any sort of ordinary
matter.
It's not planets. It's not stars. It's not
puppies. It's not black holes, even. It turns
out to be
something that doesn't absorb light, nor emit it.
The other thing we know about dark matter
is that it controls where ordinary
matter
piles up and forms galaxies, stars,
planets,
us.
So we are here in the Milky Way galaxy
because there's a huge halo of dark matter
that has so much mass that it drew in the gas
to form the galaxy in the first place.
The speculation—
very mathematically grounded speculation—
among physicists
is that the dark matter particle is the
first representative of
a whole new class of particles called
supersymmetric particles.
If the dark matter particle has the
properties predicted,
that will open up essentially a whole
new field of
physics that will help us to understand the
properties
of the stuff that we're made of, as well,
and why
our universe and everything in it
behaves the way does.
And that's dark matter.
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