[questionposter]

If black holes merge, how could that cause a gamma ray burst if light can't escape a black hole?

This post has been edited by questionposter: 9 December 2011 - 01:42 PM

[Schrödinger's hat]

The gamma rays come from in front of the event horizon, not behind it.
As matter falls into the black hole it gets compressed, heated up and pushed against other matter so much that the energy in it can be released (through nuclear reactions, and in extreme cases the matter will annihilate completely).

[Dekan]

Schrödinger, on 9 December 2011 - 01:48 PM, said:

The gamma rays come from in front of the event horizon, not behind it.
As matter falls into the black hole it gets compressed, heated up and pushed against other matter so much that the energy in it can be released (through nuclear reactions, and in extreme cases the matter will annihilate completely).

So, as the matter falls into the Black Hole, it gets heated up. When it gets hot, it must radiate heat energy outwards.

The energy would start off as infra-red, when the matter is still quite a way from the Hole. Then, as the matter gets closer to the Hole's edge, it will getter hotter, and glow red-hot. And finally, when the in-falling matter gets really close, and really hot - won't it be raised to incandescence - and shine out white-hot?

If so, I can't understand why Black Holes are supposed to be dark. Shouldn't they be very bright - shining like beacons?

[swansont]

Dekan, on 9 December 2011 - 05:34 PM, said:

So, as the matter falls into the Black Hole, it gets heated up. When it gets hot, it must radiate heat energy outwards.

The energy would start off as infra-red, when the matter is still quite a way from the Hole. Then, as the matter gets closer to the Hole's edge, it will getter hotter, and glow red-hot. And finally, when the in-falling matter gets really close, and really hot - won't it be raised to incandescence - and shine out white-hot?

If so, I can't understand why Black Holes are supposed to be dark. Shouldn't they be very bright - shining like beacons?

It's not the black hole that is bright, it's the accretion disk. And for massive black holes, this signal is skewed toward the x-ray end of the spectrum. IOW, way beyond normal incandescence.

[questionposter]

I'm not talking about quasars or accretion disks though, I'm talking about more like a gamma-ray burst out of nowhere and then astronomers assuming its black holes merging. If it was a black hole feeding on gas, we would have seen it before.

[swansont]

questionposter, on 10 December 2011 - 03:29 AM, said:

I'm not talking about quasars or accretion disks though, I'm talking about more like a gamma-ray burst out of nowhere and then astronomers assuming its black holes merging. If it was a black hole feeding on gas, we would have seen it before.

The question is what the astronomers were talking about. Gamma-ray bursts are associated with the supernova that occurs prior to formation of a black hole or neutron star, or the merger of stars, one of which is not a black hole.

http://imagine.gsfc...._l1/bursts.html
http://en.wikipedia....Gamma-ray_burst

[guenter]

Schrödinger, on 9 December 2011 - 01:48 PM, said:

As matter falls into the black hole it gets compressed, heated up and pushed against other matter so much that the energy in it can be released (through nuclear reactions, and in extreme cases the matter will annihilate completely).

What happens to the infalling matter finally is not known. Besides being compressed it is also exposed to high tidal forces. Matter-Antimatter-Annihilation however seems rather unlikely, because Antimatter doesn't fall in as far as we know. But its an interesting question, whether under high energy conditions (like in the early universe) the conservation of the baryon number could be violated. Has someone an idea?

[questionposter]

I'm still talking about specific instances where I specifically hear that merging black holes cause a gamma-ray burst, not the heating of the gas around them.

[guenter]

During the merger of black holes gravitational waves will be emitted, not electromagnetic waves. The latter depend on electric charges. But there are none, if you disregard the accretion disk.

[merc187]

couldn't black holes have not been formed but have existed since the "beggining of time" black holes are nothingness thechnically and our universe started out of nothingness so again couldn't black holes be residual spots where the big bang did not exactly penetrate or possibly be the universe collapsing into nothhingness again? sorry that had nothing to do with gamma rays.