Re: How would you explain the gas found 'blowing away' from a black hole severa

Hi, Diego,

First off, gravity depends on two things; mass and distance. The gravitational force between the Earth and the Sun, for example, depends upon the mass of the Earth, the mass of the Sun, and the distance between the center of the Earth and the center of the Sun.

Now, let's imagine that, for some inexplicable reason, the Sun were to collapse to form a black hole. What would be the effect upon the Earth's orbit? The masses of the Earth and Sun would be the same, as would the distance between their centers. So, the Earth would feel the same gravity from the Sun, and it would keep moving in the same orbit as if nothing had happened (of course, it would get really dark outside).

Why would the Sun become a black hole? A black hole is an object whose surface gravity is so strong that not even light can escape. As the Sun shrinks in the example above, the distance from the center to the surface decreases, and the surface gravity increases.

So, stars, gas, or astronauts will not be "sucked into" a black hole, so long as they don't come so close that the gravity is too strong for them to escape. There are even plenty of reason to expect gas to be "shot out" of the vicinity of a black hole.

Material such as gas that is being pulled in towards a black hole will have some rotational motion around the black hole (it's incredibly unlikely that the material would be falling exactly straight into the black hole). As the material is pulled inwards, it spins more and more rapidly. The principle is called Conservation of Angular Momentum. It's the same thing that happens when an ice skater starts a slow spin with his arms extended, and then speeds up as he pulls his arms in. Friction in the gas causes it to form a thin disk as it falls inwards, and heats the gas to very high temperatures near the black hole.

So, near a black hole, we expect to find a rapidly spinning disk of very hot gas. It is possible that the high pressures (because of the high temperatures), and the high rotational speeds cause some of the gas to be expelled from the disk rather than fall into the black hole. It is also likely that the black hole itself is spinning rapidly, and that it has a magnetic field. A magnetic field whipping through the hot gas might act somewhat like an eggbeater, flinging some of the gas away from the black hole, while also channeling it into the jets that we often see from suspected black holes.

The mechanisms for accelerating gas away from black holes, while not completely understood, are certainly effective, and do accelerate the gas to very close to the speed of light in some cases. The gas cannot, however, move at 5 times the speed of light, as you stated. Nothing can move faster than the speed of light. If, however, the jet of gas happens to be aimed almost directly towards us, and it is moving very close to the speed of light, then there is an effect of relativity that makes it appear as if the jets are moving faster than the speed of light, although it is really an illusion.