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LIGO detects most massive black hole merger to date

(www.caltech.edu)
360 points Eduard | 2 comments | 14 Jul 25 20:06 UTC | HN request time: 0s | source
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perdomon ◴[14 Jul 25 20:19 UTC] No.44564794[source]▶
What happens when black holes collide? Does one black hole “consume” the other? Do they become a larger black hole? Does it get more dense or just larger?
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hnuser123456 ◴[14 Jul 25 20:31 UTC] No.44564906[source]▶
They become a larger black hole, mostly conserving mass, minus a few percent to gravitational waves. However, their mass is proportional to their radius, not volume, so it gets LESS dense. If you laid out a bunch of black holes in a line, just barely not touching, and let them merge, suddenly, the whole sphere of space enclosing the line becomes black hole. It also turns out that a black hole with the mass of the universe would have a volume about the size of the universe.
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JumpCrisscross ◴[14 Jul 25 20:44 UTC] No.44565021[source]▶
> turns out that a black hole with the mass of the universe would have a volume about the size of the universe

Mass and energy.

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gjm11 ◴[14 Jul 25 20:53 UTC] No.44565141[source]▶
Is that intended to be a correction? (I don't think the original statement needs correcting, other than by replacing "universe" with "observable universe" in both places.)
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hnuser123456 ◴[14 Jul 25 21:03 UTC] No.44565260[source]▶
Up until the universe was around a few billion years old, its Schwarzchild radius would have been larger than even the co-moving (not just observable) universe's radius, but the initial momentum from the big bang was high enough to prevent collapse.
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AnimalMuppet ◴[14 Jul 25 22:16 UTC] No.44565946[source]▶
That sounds suspiciously like "they were inside a region with enough mass to form an event horizon, but they escaped because they had enough momentum", which in turn sounds like "we can escape from inside an event horizon if we just move fast enough". Can you explain how that's not what you're saying?
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1. hnuser123456 ◴[14 Jul 25 22:29 UTC] No.44566046[source]▶
I wish I had a straightforward answer to that. I'm sure the answer is some combination of cosmic inflation and dark energy, but by all means it appears the early universe either narrowly escaped, or simply is a black hole, that singularities are a flawed concept, that nothing is escaping the universe, and we are all stuck moving forward in time, and that the infinite future is the singularity.
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2. AnimalMuppet ◴[15 Jul 25 00:23 UTC] No.44566697[source]▶
I don't have an answer either. But in my amateur opinion, of the available options, I lean toward "is a black hole". If all the mass we can see adds up to a black hole the size of what we can seen, then if you add all the stuff outside the light cone, it should add up to enough mass to make a black hole radius that includes the distance out to there.

But that leaves us with black holes forming inside a black hole, which I have absolutely no idea what to do with.