Supermassive black holes with up to 10 billion
times the mass of our sun are thought to be
at the center of most large galaxies.
As their powerful gravity sucks in material,
they can create a ring of superheated matter
brighter than the galaxy itself called a quasar, and
astronomers long thought that this was the
signal of a galaxy’s demise.
But the recent discovery of cold quasars has
changed how we think galaxies end their life cycles.
A ring around a pitch black hole that’s
brighter than a whole galaxy is quite a contrast,
but it’s what happens when dust and gas
falling into the black hole starts swirling
at nearly the speed of light.
At these extreme speeds, the friction between
the particles superheats the material, giving
off X-rays.
Because quasars are so bright and can be seen
from so far away, they look almost like stars,
hence the name, which comes from “quasi-stellar
radio source.”
To astronomers, a quasar is the sign of a
passive dead galaxy where no more stars will form.
That’s because the magnetic field surrounding
the gas can get twisted up, steering gas away
from the black hole and launching it into
space, shutting off the gas supply the galaxy
needs to form new stars.
Quasars only last as long as their fuel source
allows, and after they run out of gas a faint
galaxy is all that’s left behind.
But just maybe, somewhere in that span, the
galaxy gets one last hurrah.
Astronomers decided to check if star formation  
in galaxies with quasars might be possible.
They first picked out an area of the night
sky with visible quasars.
They honed in on blue ones because those are
passed a phase where dust surrounding them,
that’s still cool, absorbs their radiation
and turns them red.
So these were galaxies that should be at the
end of their lives.
Then they looked at those blue quasars with
both an X-ray and a far infra-red telescope.
X-rays are the sign of superhot material,
like the gas falling into a black hole.
But infra-red radiation shows just the opposite;
cool gas that’s still capable of clumping
together and forming stars.
Unexpectedly, they found both X-ray and infra-red
signatures in about 10% of the quasars they
looked at.
That is completely contradictory to how we
thought this worked.
Somehow, this minority of galaxies still had
pockets of cool gas left in them, and they
came in all galactic varieties, like spiral
and elliptical and compact.
The astronomers think they may have gotten
very lucky, catching these galaxies in a transition
phase that may be as short as 10 million years.
I know that seems like a long time, but on
a universal timescale that’s barely a hiccup.
The astronomers behind the discovery likened
this period to a little retirement party before
the galaxy calls it quits, which is completely
adorable.
So do all galaxies get a gold watch and a
few more stars before shutting up shop, or
is this a rare phenomenon?
That’s what the researchers are trying to
figure out next.
I for one hope it happens to all galaxies,
even our Milky Way, because I’m really hoping
this retirement party has cake.
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The astronomers made this discovery while
conducting what they call a “blind survey,”
hoping to find objects they weren’t looking for.
It pays to go into things with an open mind.
If you liked this video, check out this one
I did on the Fulton Gap.
And for more science in your day, make sure
to subscribe and thanks for watching for Seeker.
