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.