Observing black holes

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Observing black holes

#1  Postby Greg the Grouper » Aug 24, 2022 7:31 pm

The other day, some of my coworkers were talking about how light interacts with black holes, and though it took me a week or so, I finally got around to thinking about it.

I assume to some degree that there exists light particles orbiting black holes in much the same way that we have satelites orbiting the earth; light hits a unique point in the black hole's orbit where the gravitational pull of the black hole causes light to curve around the black hole, while causing the light particles to accelerate enough such that their momentum keeps them from reaching the surface of the black hole. Or something like that, I'm no physicist.

That being approximately the case, would a black hole appear visually to an outside observer like a star? Could one reasonably distinguish through visuals between a light sink where particles are trapped in its orbit versus an actual source of light?
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Re: Observing black holes

#2  Postby The_Piper » Aug 25, 2022 12:58 am

I think that light just bends around it and continues on it's way. Outside of the event horizon light is traveling too fast to be caught up in orbit. Black holes that are "feeding" like the supermassive black holes at the center of galaxies have what's called an accretion disk, made up of matter orbiting the black hole, which is giving off light. From a distance to the naked eye they are lit up like stars. There are solar-mass black holes that aren't accreting any matter, and they are invisible.
Here is an image of the black hole at the center of the Messier 87 galaxy, that was compiled over time, using modern techniques. I'm unaware off the top of my head how they did it. Image
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Re: Observing black holes

#3  Postby Spearthrower » Aug 25, 2022 2:57 am

The mass of the black hole warps spacetime and causes the light's path to bend around it. This can make far away stars or galaxies appear much brighter than they should thanks to the gravitational lensing effect.

Other means of observing them are the effect they have on other visible physical matter nearby, accreting dust, or ripping stars apart.
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