LIGO Black hole merger may have optical confirmation

https://www.caltech.edu/about/news/black-hole-collision-may-have-exploded-light

by throwaway2048 • 6 years ago

93 10 6 years ago

number62• 6 years ago

How strange that "Seeing is believing" still holds even with gravitational waves, which aren't electromagnetic phenomena. Human nature :)

redis_mlc• 6 years ago

The LIGO concept was thought to be impossible for decades because of how small the signals are, and some would say it's still incredible that it works at all.

Whereas we've had a lot of success with optical detection and they're inexpensive experiments.

Also, there's a few naysayers continually making public comments, so it's good to have something else to point to for confirmation.

willis9362• 6 years ago

Two point verification always has value. It’s how every instrument we’ve ever made is calibrated.

number62• 6 years ago

Can gravitational waves be verified by optical signals? I thought the whole point of LIGO is that it's a method not relying on electromagnetic signals

cletus• 6 years ago

I don’t understand the surprise or confusion here. Yes, light can’t escape black holes. But black holes are systems And they typically would have accretion disks. Those very much could emit light (and no doubt a ton of X-rays and/or gamma rays) when the black holes “collide” (as violent and energetic as these events are, I think “merge” is still probably more accurate).

The magnitude of these events is simply mind-boggling. I think the first such LIGO detection has an estimated 3-5 Solar masses converted to energy.

volodymyrs• 6 years ago

the surprise is that to make an accretion disk which would make any detectable emission, there had to be a lot of matter around a black hole.

the accretion disks are commonly seen around binaries consisting of a stellar mass black hole and a regular star. stars feeds the disk in this case.

another possibility is to have a supermassive back hole in the galaxy center, which feeds on the surrounding gas, making much larger and slowed disk.

what has never been seen before a stellar mass black hole (or pair of black holes) feeding on the interstellar medium. This should happen of course, but the expected luminosity is way below anything detectable.

binary black hole, i.e. a system without any addition mass to accrete, would have to be in some very unusually dense medium, and the medium would need to be disrupted by merger.

interestingly, such medium can occur around another back hole - a supermassive one.

wcoenen• 6 years ago

Once the black holes merge, the new, now-larger black hole experiences a kick that sends it off in a random direction, and it plows through the gas in the disk

Hm, I would expect the merged object to move in the same way as the center of mass of the unmerged objects. Where does the extra momentum for this "kick" come from? Is there mass from the surrounding disk thrown in the other direction? Or maybe some relativistic effect?

edit: apparently gravitational waves can carry away linear momentum, and that's where the kick comes from[1].

[1]https://astrobites.org/2018/03/08/recoil-detectives-searchin...

LIGO Black hole merger may have optical confirmation

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