Astronomy/black hole

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Question
i have a question on black hole,some prof says blackhole is a new dimesion some say its empty what realy is it,what itside it if there nothing then what about gravity isnt that somethibg if there nothing in there then how it sucks thing in,it must take all those thing that it suck somewhere right,it can just get in there a disappere to dust or whtever..s0 what realy is it?

Answer
Black holes are regions of essentially normal space, except for one thing. At their center they have an object of some mass but essentially zero size, crushed to that size by its own gravity. Most black holes are the remnants of "dead" massive stars that blew most of themselves to bits in a supernova explosion, but some substantial mass remained and collapsed to zero size, creating a "black hole" in the process.

Under normal circumstances there isn't anything inside the black hole except the point mass at its center, so there is no obvious "boundary" for the thing. The only thing that distinguishes it from the normally empty space surrounding it is that if you are far enough from the central mass, the "escape velocity" required to get away from the thing is less than the speed of light, so no matter how difficult it might be to avoid falling into the hole it is at least theoretically possible. However, if you are at or inside a distance from the center called the Schwarschild radius, then the gravity of the central body is so large that nothing, including light, can escape, and anything inside that distance will (fairly quickly) fall into the center and become part of the central mass.

There are circumstances in which the inside isn't empty other than for the mass at the center, namely when some nearby object (or objects) are losing mass, and the lost mass is falling into the black hole. Under those circumstances the inside of the black hole would be filled with whatever material happens to have fallen in so recently that it has not yet had time to reach the central point. But such circumstances can only last for relatively short periods of time, so most of the time there is nothing inside or near the black hole save for the central point.

To answer the last part of your question, about what the stuff that falls in is like, usually it is just gas, and stays that way until it gets pretty close to the central point; but no matter what it is it is subject not only to the overall gravitational pull that is causing it to inexorably fall to the center, but also to tidal forces that tend to pull the parts of it that are closer to the center away from the parts that are further away. Very close to the center (within a few atomic diameters or so of the exact center) the tidal forces are so large that they can pull the atoms apart, then the pieces of atoms apart, and so on, until whatever falls into the center and becomes part of the central mass is unlike anything ever encountered in normal space.

Questions such as this, even if perfectly answered, tend to raise a host of additional questions; so if there is any part of this that you need me to better explain or you would like me to elaborate on, just let me know and I'll be happy to do what I can to help.

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Courtney Seligman

Expertise

I can answer almost any question about astronomy and related sciences, such as physics and geology. I will not answer questions about astrology and similar pseudo-scientific rubbish.

Experience

I have been a professor of astronomy for over 40 years, and am working on an online text/encyclopedia of astronomy, and an online catalog of NGC/IC objects.

Publications
Astronomical Journal, Publications of the Astronomical Society of the Pacific (too long ago to be really relevant, but you could search for Courtney Seligman on Google Scholar)

Education/Credentials
I received a BA in astronomy and physics and a MA in astronomy, both from UCLA. I was working on my doctoral dissertation when I started teaching, and discovered that I preferred teaching to research.

Awards and Honors
(too long ago to be relevant, but Phi Beta Kappa and Sigma Xi still keep trying to get me to become a paying member)

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