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Just about every galaxy has a supermassive
black hole at its center,
one millions of times the mass of the Sun.
It’s been hard nailing down exactly how
many smaller black holes there are out there, though,
especially near galactic centers,
because black holes are hard to see.
But a paper published last week in the journal
Physical Review Letters
has new insight about where we can look to nail that number down.
The secret?
Black holes of a feather orbit together.
Black holes look… black.
They’re so dense that even light can’t
escape from them,
so directly detecting one is nearly impossible.
We can still find them through gravitational
effects, though,
and through X-ray light given off by objects that heat up before falling into them.
But it’s been a challenge to use those measurements
to estimate how many less massive black holes are out there,
ones with masses like the Sun’s.
Earlier this year, a study of X-ray sources
in the Milky Way
suggested that there might be as many as ten or twenty thousand smaller black holes near our galaxy’s center.
And a similar study of ring galaxies, the
beautiful results of galactic collisions,
found evidence for lots of small black holes, too.
But new simulations have given us a much better
idea of where to look for them next.
In last week’s paper, a pair of Hungarian
physicists made a new computer model of small stars, heavy stars, and black holes
all orbiting near the center of a galaxy like the Milky Way.
They ran their program for millions of simulated years,
enough time for everything to finish jostling for position and get settled.
Once that was all over, they found that low-mass
stars ended up with all sorts of orbits,
different sizes, different angles, you name it.
Together, they created a big, bright sphere
of stars around the galactic center,
which is pretty much what we see in actual galaxies.
The black holes, though, did something more
interesting.
All the pushing and shoving before orbits
settled down tended to push them all into one plane,
a lot like how all the planets
in our solar system orbit in a single, flat disk.
The same happened to heavier stars, which
we’ve seen in the actual Milky Way.
But we didn’t know it would happen with
black holes, too.
Now, that insight could help target our searches
for black holes near the center of the galaxy,
learning where they are and what they’re
doing more quickly than we could through general surveys.
Meanwhile, in other black hole news, sort
of, scientists are getting one step closer to totally understanding supernovas.
Most black holes form from supernovas:
colossal explosions of dying stars that launch heavy elements throughout the universe.
So far, we have a good idea of what happens
in the chaos of a supernova,
but there are still some details to work out and some measurements we need to make
before we’re completely confident in our models.
The good news is, a paper in last week’s Nature Astronomy has helped us check one item off that list:
understanding a small flash
before the main explosion.
The paper’s authors looked at Type II supernovas.
These start when a massive star begins to
run out of nuclear fuel,
and its gravity starts pulling everything in toward its center.
As things get denser, protons and electrons
in the star’s core combine into neutrons,
creating an incredibly dense neutron star.
Then, when the original star’s outer layers
collide with the edge of that inner neutron star,
they violently bounce off, creating
an explosion that can outshine an entire galaxy.
Before that main explosion, though, we’ve
also seen a smaller flash.
We’ve only observed them a couple of times,
but we think they should happen before pretty much every Type II supernova.
We’ve just never been able to confirm that,
because we haven’t had instruments sensitive enough and haven’t looked long enough to catch them all.
That’s where this new paper helped.
Using a telescope in Chile equipped with one
of the highest-resolution cameras in the world,
these researchers watched that process unfold
on 26 different Type II supernovas.
And they found a flash of light before most
of the main explosions.
That confirmed those flashes are a regular
thing.
But then, the authors went further.
We already knew that for thousands of years
before a supernova,
some of the star’s atmosphere leaks into space,
leaving a bunch of gas hanging
around when the star finally does start collapsing.
We think the flashes happen when some of the
energy from the formation of the neutron star
sneaks out and hits this gassy layer before
the energy of the rebounding gas does.
But we haven’t had a good idea of how much
gas is actually out there
because we’ve seen so few of these flashes.
So this paper’s authors worked with an existing
model of supernovas to figure it out.
They found that, to make the flashes they
observed,
the star would need to lose as much gas as you’d find in our entire Sun before becoming a Type II supernova.
Which goes to show you how huge these stars
are to begin with.
They’re some of the biggest ones in the
universe.
That’s a lot of gas.
But it’s only enough to create a tiny flash
that we hardly noticed before,
because it then gets drowned out by the supernova itself.
With bigger and better telescopes coming online
all the time,
and with models that are constantly being improved by research like this,
we should be seeing more and more of these flashes as time goes on.
And that means we should gain a better and
better understanding of what happens in some of the universe’s largest explosions.
Thanks for watching this episode of SciShow
Space News!
There’s a lot happening in the universe,
and if you want to learn about the latest news in planets, moons, black holes, and everything else,
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