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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 en

by spuz 9y ago

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?

T-A 9y ago
If you accelerate an electric charge, it emits electromagnetic waves. If you accelerate a mass, it emits gravitational waves. Two masses orbiting their common center of gravity are undergoing centripetal acceleration, so they continuously emit gravitational waves, spiraling closer as they lose energy (that's how the emission of gravitational waves was originally confirmed [1]). [1] https://www.nobelprize.org/nobel_prizes/physics/laureates/1993/speedread.html https://www.nobelprize.org/nobel_prizes/physics/laureates/19...
evanb 9y ago
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 sloshing mass around. Where did the photons "come from"? Well, they weren't stored "inside" the electrons. By what process were the photons generated? Electrons accelerating radiate. That's essentially the answer. You can "math it up" if you want. It's not exactly an axiom, but it's pretty close to the bottom.
- evanb 9y ago
  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 to a co-rotating frame.
  - raverbashing 9y ago
    > 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 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.
    - improbable22 9y ago
      Certainly normal matter (like the earth) has mass and warps spacetime. But a black hole is a purely gravitational object, there need not be any normal matter involved. 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.
      - raverbashing 9y ago
        > But a black hole is a purely gravitational object, there need not be any normal matter involved. There's no "purely gravitational object" it only "looks like that" from behind the event horizon We know the escape velocity > c and that's pretty much it, for GR it's a singularity (which usually means the theory is incomplete in that circumstance) and we don't know how QM work when squeezed harder than a Neutron star > The mass of a black hole is something that's really only defined from a distance away. If you mean "we can sense the gravitational field of something having mass X at a distance D larger than the event horizon" I agree. But I'd rather say "we don't know what happens there" instead of "singularity" (which is what the current theories say it's inside and from the point of view of Relativity they're not wrong)
        evanb 9y ago

by spuz 9y ago

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?

T-A 9y ago

If you accelerate an electric charge, it emits electromagnetic waves. If you accelerate a mass, it emits gravitational waves. Two masses orbiting their common center of gravity are undergoing centripetal acceleration, so they continuously emit gravitational waves, spiraling closer as they lose energy (that's how the emission of gravitational waves was originally confirmed [1]). [1] https://www.nobelprize.org/nobel_prizes/physics/laureates/1993/speedread.html https://www.nobelprize.org/nobel_prizes/physics/laureates/19...

evanb 9y ago

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 sloshing mass around. Where did the photons "come from"? Well, they weren't stored "inside" the electrons. By what process were the photons generated? Electrons accelerating radiate. That's essentially the answer. You can "math it up" if you want. It's not exactly an axiom, but it's pretty close to the bottom.

evanb 9y ago
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 to a co-rotating frame.
- raverbashing 9y ago
  > 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 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.
  - improbable22 9y ago
    Certainly normal matter (like the earth) has mass and warps spacetime. But a black hole is a purely gravitational object, there need not be any normal matter involved. 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.
    - raverbashing 9y ago
      > But a black hole is a purely gravitational object, there need not be any normal matter involved. There's no "purely gravitational object" it only "looks like that" from behind the event horizon We know the escape velocity > c and that's pretty much it, for GR it's a singularity (which usually means the theory is incomplete in that circumstance) and we don't know how QM work when squeezed harder than a Neutron star > The mass of a black hole is something that's really only defined from a distance away. If you mean "we can sense the gravitational field of something having mass X at a distance D larger than the event horizon" I agree. But I'd rather say "we don't know what happens there" instead of "singularity" (which is what the current theories say it's inside and from the point of view of Relativity they're not wrong)
      - evanb 9y ago