Black Holes And Light

[David Jerome]

I was informed in another thread that the "supermassive black hole" in the middle of our galaxy doesn't swallow us up, because of forward moment that causes us to orbit the black hole, rather than get sucked into it.

Okay.

But the gravity from a black hole is powerful enough to keep light from escaping. That being the case...why aren't there swirls of light orbiting black holes, the way the stars orbit the black hole at the center of the galaxy?

 

[freezerman2000]

The SMBH at the center of our galaxy is in the middle of the most densely packed region of the galaxy.
Those further out do not have such numbers of stars to feed upon.Astronomers can detect them through the erratic orbits of stars around them.
Some black holes also appear to go dormant (not feeding).

 

[Wiccan_Child]

I was informed in another thread that the "supermassive black hole" in the middle of our galaxy doesn't swallow us up, because of forward moment that causes us to orbit the black hole, rather than get sucked into it.

Yup. It's the same basic principle why the Moon doesn't crash into the Earth, or the Earth into the Sun. Technically, we're always 'falling' into it, but we're also moving forward, and the mechanics of it means that it all balances out.

But the gravity from a black hole is powerful enough to keep light from escaping. That being the case...why aren't there swirls of light orbiting black holes, the way the stars orbit the black hole at the center of the galaxy?

Ah, but there are! Black holes have a peculiar phenomenon around them called the photon sphere (and, in the case of charged black holes, two photon spheres).

If you're imagining light being pulled into a black hole in such a way that it 'orbits' it... there are problems with that scenario. It's technically possible, but because light can't slow down, it has to come in at the black hole at preciesly the right angle, otherwise it will quickly degenerate and either spin in or out. By contrast, a stable planetary orbit forms for two reasons: first, planets can change their velocity, and second, they form from already orbiting clouds of dust, so any clumps that begin to fall away simply do - the planet is the aggregate of those bits of matter which happen to fall into a stable orbit.

And since light doesn't aggregate, you wouldn't only get isolated photons, if that.

 

[Michael]

But the gravity from a black hole is powerful enough to keep light from escaping. That being the case...why aren't there swirls of light orbiting black holes, the way the stars orbit the black hole at the center of the galaxy?

FYI, when they "feed", they form "jets" at both poles. This is a jet from M87.

http://www.holoscience.com/wp/wp-content/uploads/2008/05/M87-jet.jpg

As WC points out, photons would need to be extremely lucky to stay in orbit and they wouldn't remain stable anyway since material flows in, and energy flows in all the time. Black holes can even be "charged" to some degree and their motion create EM fields around them. Assuming a few lucky photons remained in a stable orbit for any time, you'd never see them.

FYI, this is a nice YouTube video on the black hole in the center of our galaxy.

http://www.youtube.com/watch?v=KCADH3x56eE

 

[hericles]

The gravitional pull of black holes (even super massive black holes) only exert such a pull when objects have passed the event horizon. Light beams outside the event horizon still maintain enough velocity to escape the pull of the black hole.

 

[Tiberius]

I was informed in another thread that the "supermassive black hole" in the middle of our galaxy doesn't swallow us up, because of forward moment that causes us to orbit the black hole, rather than get sucked into it.

Okay.

As long as we are outside the event horizon, it's just another object with mass, and it can be orbited just the same way you;d orbit a planet.

But the gravity from a black hole is powerful enough to keep light from escaping. That being the case...why aren't there swirls of light orbiting black holes, the way the stars orbit the black hole at the center of the galaxy?

Because the swirls of light are caught in the gravity. For them to escape so we could see them, they'd have to be in a place where they aren't caught in the gravity.