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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 lookblack.

  • 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,

  • you can go to youtube.com/scishowspace to subscribe.

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B1 black star supernova galaxy milky galactic

The Milky Way May Have a Disk of Black Holes

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    林宜悉 posted on 2020/03/30
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