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  • Supermassive black holes are thought to be at the center of most galaxies, and they are

  • huge.

  • The Milky Way's own supermassive black hole, Sagittarius A*, is about 4 million times the

  • mass of our sun.

  • But scientists have just spotted two absolute behemoths, that dwarf Sagittarius A*,

  • and they are on a collision course.

  • It's the first time such massive black holes have been spotted this close together, and

  • it could help us detect a hum of gravitational background noise.

  • Of coursecloseis a relative term and in this particular instance when scientists

  • say close, they mean about 1,400 light-years apart.

  • The black holes are located about 2.5 billion light-years from us, so since the light from

  • them took 2.5 billion years to reach us, we're observing them as they were 2.5 billion years ago.

  • Coincidentally, the scientists who discovered them estimate that that's about how long

  • it will take before they collide.

  • They could be going all smashy smashy right now, unleashing huge gravitational waves millions

  • of times more powerful than those previously detected by LIGO and Virgo.

  • Of course, because of how far away they are, the waves won't reach us for 2.5 billion

  • years.

  • That is, if they happen at all.

  • We've observed stellar mass black holes merging, but we're not sure if their supermassive

  • counterparts can join forces megazord-style too.

  • It seems odd, I mean, these things each have an incredible gravitational pull, why wouldn't

  • they ram head on into each other?

  • Right now the thinking is when galaxies merge, their supermassive black holes begin to orbit

  • each other.

  • As they do, dust and stars in between them sap some of their energy, causing their orbits

  • to tighten.

  • But as they get closer, that region of space between them shrinks, until theoretically

  • there's no way to lose more energy.

  • The two black holes find themselves stably orbiting each other but never getting closer,

  • like you and your crush at an 8th grade dance.

  • Some studies suggest that happens at about 1 parsec, or roughly 3.2 light-years distance,

  • so it's known as the final parsec problem.

  • But all that is theoretical, and we're lacking more observational data.

  • It's possible our predictions are wrong and black holes of this size do merge instead

  • of stalling out a parsec apart.

  • Unfortunately, black hole pairs are very hard to spot.

  • Remember how I said this is the closest we've seen two this big and they're 1,400 light-years

  • away from each other?

  • 1 parsec is way too close for us to distinguish two supermassive black holes apart.

  • And now that we've found these two, it's not like we can wait around 2.5 billion years

  • to see if they merge.

  • I'll probably be dead by then.

  • But since we've spotted these two, we can start to guess how common merging supermassive

  • black holes would be.

  • Based on their findings the scientists estimate that optimistically there are 112 black holes

  • whose gravitational waves we can detect from Earth.

  • This would make a kind of constant hum, the scientists likened this gravitational background

  • noise to a chorus of chirping crickets.

  • Normally it'd be impossible to distinguish one cricket from another.

  • But if there's no final parsec problem and they can merge, it should create a massive

  • chirp at the moment they collide.

  • When that happens, the waves will be at frequencies outside what LIGO and Virgo can detect.

  • So instead, scientists will have to keep a close eye on pulsars, special stars that send

  • out radio waves at regular intervals.

  • If a supermassive merger stretches or compresses the space between us and a pulsar, the rhythm

  • will appear to be thrown off.

  • These frequency changes are so small, just tens to hundreds of Nanohertz,

  • it will require close to a decade of observation to spot the weak signal hiding in the noise.

  • They're searching for more pairs of black holes to refine their prediction further,

  • but it's possible we never detect a merger and the final parsec problem is insurmountable

  • after all.

  • Thanks for watching, don't forget to subscribe for more videos, like Amanda's here on what

  • a black hole actually looks like.

  • And while LIGO can't detect supermassive mergers, it was recently upgraded, making

  • it 40% more sensitive as it continues its hunt for merging stellar mass black holes.

  • Well that's all for now, I'll see you next time on Seeker.

Supermassive black holes are thought to be at the center of most galaxies, and they are

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科學家剛剛檢測到兩個超大品質黑洞在相撞的過程中 (Scientists Just Detected Two Supermassive Black Holes on a Collision Course)

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    林宜悉 發佈於 2021 年 01 月 14 日
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