31–40 of 70 posts
Interesting This was a couple of days days before Virgo got online AND one of the Ligo detectors was undergoing a noise modelling test (its mirrors were being vibrated at the time)
So no second opinions then, it could just as well be noise?
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None of this actually answers the question. The question is by what process does energy in the binary black hole system get converted into gravitational wave energy?
The answer is "by the processes of general relativity". When things fall "down" their potential energy is lowered, so they get faster. When mass-energy accelerates it emits gravitational waves, in much the same way when an electron accelerates it emits electromagnetic waves. If you're satisfied that a radio works by sloshing electrons around, you should be satisfied that a black hole merger emits radiation by sloshin…
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Anything spinning in an asymmetrical way (e.g. two bodies orbiting each other, but not a single body spinning) loses angular momentum as gravity waves. This is true whether it's two black holes or a tumbling dumbbell. In addition to that, the ultimate merger of the black holes releases the incredible amount of gravitational potential energy that existed between them when they were separate bodies. No mass escapes the…
> No mass escapes the event horizon. These are black holes after all :) OK, that makes sense (for whatever that's worth). But from the article: > ... the latest discovery was produced by the merger of two relatively light black holes, 7 and 12 times the mass of the sun ... The merger left behind a final black hole 18 times the mass of the sun, meaning that energy equivalent to about 1 solar mass was emitted as gravit…
With two well-separated black holes it's reasonable to talk about each of their rest masses, and the potential, just like the apple. But as they get close and merge these ideas are hard to pin down, and stop being useful. Their shapes get blended together, and their horizons unite into one sphere, and for a while this wobbles around a lot before settling down. Some of the energy of its wobbling around departs as gravitational waves. Once it's settled down you can meaningfully talk about its rest mass again.
Earlier quoted context omitted.
Anything spinning in an asymmetrical way (e.g. two bodies orbiting each other, but not a single body spinning) loses angular momentum as gravity waves. This is true whether it's two black holes or a tumbling dumbbell. In addition to that, the ultimate merger of the black holes releases the incredible amount of gravitational potential energy that existed between them when they were separate bodies. No mass escapes the…
How much of the 1 solar mass of detectable gravitational energy is released before the moment of collision and how much is released at the moment of collision? Is the mechanism for release of this energy the same in both cases? If 1 solar mass of energy was released in total, and the mass of the combined black hole is less than the two before the merger, how is it possible that none of the mass of the black holes has…
The missing mass is precisely the amount of energy that was radiated away.
We should not think of the mass of the black hole as being the amount of matter stored inside, which may escape... regardless of how it was created, the black hole is just a ball of pure gravity. Its mass is defined by its effect on things far away. You can measure the mass of Jupiter by watching how fast a satellite orbits, and a black hole whose satellites had the same orbits would be said to have the same mass.
Earlier quoted context omitted.
The answer is "by the processes of general relativity". When things fall "down" their potential energy is lowered, so they get faster. When mass-energy accelerates it emits gravitational waves, in much the same way when an electron accelerates it emits electromagnetic waves. If you're satisfied that a radio works by sloshing electrons around, you should be satisfied that a black hole merger emits radiation by sloshin…
Maybe I should be more clear: at least in the generally relativistic conception of gravity, all of the mass of the black hole "comes from" the warping of spacetime already. That's why I keep dancing around the question of whether it's "really" the kinetic energy or the mass or a mix that gets converted---it's hard to distinguish and may not be meaningful to distinguish the pieces from one another, especially if I go…
No, it's the other way around. The warping is due to the mass
But the other answer hinted at the source: accelerating mass turns into gravitational waves as an accelerating electron turns into EM waves (remember rotation and things stopping abruptly also means acceleration)
So yeah, it's the potential energy that turns into (less than Newtonian amounts of) kinetic energy because some of it is turning into Gravitational waves
And you can imagine something as big as black holes spinning around each other at a frequency measurable in Hz how much energy they can give in that process then add the sudden merger deceleration.
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> No mass escapes the event horizon. These are black holes after all :) OK, that makes sense (for whatever that's worth). But from the article: > ... the latest discovery was produced by the merger of two relatively light black holes, 7 and 12 times the mass of the sun ... The merger left behind a final black hole 18 times the mass of the sun, meaning that energy equivalent to about 1 solar mass was emitted as gravit…
For black holes these aren't separate concepts. An apple and the earth each have rest mass, and gravity means there is also potential energy in their separation. But a black hole is an object with rest mass which is made purely out of gravity. With two well-separated black holes it's reasonable to talk about each of their rest masses, and the potential, just like the apple. But as they get close and merge these ideas…
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> I believe that black hole mergers are dark in the entire electromagnetic (EM) spectrum. Now that I think about it - yes, of course. It's why they are called _black_ holes. ;-) facepalm
That doesn't follow from the fact that black holes are "black". For example, black holes can emit a ton of radiation from accretion disk as matter accelerates and falls inwards, radiating huge amounts of energy [0]. Two naked black holes merging probably wouldn't emit much (if any) EM radiation, but if they had very active accretion disks, then it's certainly possible there would be a ton of EM activity. [0] https://…
I am not sure, though, if regular (stellar-mass) black holes with an accretion disk emit enough EM radiation to be visible at such distances, or if it would become lost among the radiation emitted by the rest of the galaxy.
(A merger between two supermassive black holes with active accretion disks must be a spectacular sight even from a safe distance.)
> Dubbed GW170608, the latest discovery was produced by the merger of two relatively light black holes, 7 and 12 times the mass of the sun, at a distance of about a billion light-years from Earth. The merger left behind a final black hole 18 times the mass of the sun, meaning that energy equivalent to about 1 solar mass was emitted as gravitational waves during the collision. I wonder if one would experience any macr…
Was it all emitted as gravity waves? Given the forces I'd assume that some of it may have been emitted as radiation (acceleration/heating of any surrounding matter etc). And I'm waiting for someone to prove that something might even escape from either of the holes during the final spin. There must be a moment where the two event horizons balance each other out + spinning = potential for very strange things. Maybe, like two bubbles merging, some smaller holes could have pealed off.
Earlier quoted context omitted.
For black holes these aren't separate concepts. An apple and the earth each have rest mass, and gravity means there is also potential energy in their separation. But a black hole is an object with rest mass which is made purely out of gravity. With two well-separated black holes it's reasonable to talk about each of their rest masses, and the potential, just like the apple. But as they get close and merge these ideas…
OK, but what about the event horizon issue? So some stuff (GM) can escape the event horizon, but other stuff (matter, light) can't escape. So they must somewhat be separate concepts, because the event horizon affects them differently.
The fact that we can get away with studying only the exterior is really the same fact that the horizon is a horizon. The causality only goes one way, for everything not just for normal matter. And thus ignorance of the interior is no barrier to understanding the exterior.
Earlier quoted context omitted.
Maybe I should be more clear: at least in the generally relativistic conception of gravity, all of the mass of the black hole "comes from" the warping of spacetime already. That's why I keep dancing around the question of whether it's "really" the kinetic energy or the mass or a mix that gets converted---it's hard to distinguish and may not be meaningful to distinguish the pieces from one another, especially if I go…
> all of the mass of the black hole "comes from" the warping of spacetime already No, it's the other way around. The warping is due to the mass But the other answer hinted at the source: accelerating mass turns into gravitational waves as an accelerating electron turns into EM waves (remember rotation and things stopping abruptly also means acceleration) So yeah, it's the potential energy that turns into (less than N…
The mass of a black hole is something that's really only defined from a distance away. If a planet of 1 earth-mass orbits it at the same speed & circumference as we do the sun, then we say the black hole has 1 solar mass.