Black Holes

[Greg]

do or dont black holes exsist.if so is it true that a black hole is a exploded star or planet that exploded under its own gravity. and has shunk to a small spec in space and has the gravity of 1000 times that of earths.

[Buffy]

Do. The original object must be at least 3 solar masses (3 times as much stuff as our sun), and thus has to be a star. When it collapses, it throws off a bunch of stuff, but its still going to be almost as big as it was before it started in mass, which yes, is going to be much more than "1000 earths" but is going to be at least as big as the original object. There is good evidence that the center of our and many other galaxies have supermassive black holes that have sucked in lots of other gunk over time, so they are really, really, unbelievably big, big, big.

Cheers,
Buffy

[Vishesh]

Thats right,Buffy. I remember watching the Discovery channel last month and they explained how it was discovered that many known galaxies (including Andromeda) have blackholes at the centre.These black holes have mysteriously stoped sucking in gases from space.

There are even some theories saying that these black holes are the objects responsible for the 'birth' of galaxies.


See you later,
Vishesh

[Boerseun]

Interesting things, black holes.

One thing that I don't quite get, though, it that seeing as nothing can escape a black hole, ever, according to the Laws of Nature, how is the Big Bang scenario possible? 'Cause the idea is that all the stuff in the Universe was compressed into a little speck which exploded, and... you all know the story. That just means that either the Laws of Nature evolved together with the Universe, say, in the first couple'o seconds, or stuff can actually escape a black hole. 'Cause if everything was in the original singularity, that must have just been one hell of a black hole?
Or could there be mass limits to black holes? Say, a black hole can have 10,000 solar masses, for the sake of the argument, but at 10,001 some sort of repulsive force will blow it apart, overcoming the gravitational attraction?
The only thing I can think of, if the Big Bang hypothesis is to be believed, is that the Laws of Nature must somehow have been in flux initially. That's probably why we can't say for sure where all the stuff came from in the first place, cause there's no way to experiment with the original set of Laws.
Hmmmmmmm...

[Tormod]

Originally Posted by Boerseun

The only thing I can think of, if the Big Bang hypothesis is to be believed, is that the Laws of Nature must somehow have been in flux initially. That's probably why we can't say for sure where all the stuff came from in the first place, cause there's no way to experiment with the original set of Laws.

This is basically correct. In standard cosmology the laws of nature are a result of the Big Bang, so they would not have been the same before.

However, in string theory things are slightly different (for example, they have no singularity at the beginning of time) so they even talk about t-x (ie, the time before the Big Bang).

[infamous]

Originally Posted by Boerseun

Interesting things, black holes.

One thing that I don't quite get, though, it that seeing as nothing can escape a black hole, ever, according to the Laws of Nature, how is the Big Bang scenario possible? 'Cause the idea is that all the stuff in the Universe was compressed into a little speck which exploded, and... you all know the story. That just means that either the Laws of Nature evolved together with the Universe, say, in the first couple'o seconds, or stuff can actually escape a black hole. 'Cause if everything was in the original singularity, that must have just been one hell of a black hole?
Or could there be mass limits to black holes? Say, a black hole can have 10,000 solar masses, for the sake of the argument, but at 10,001 some sort of repulsive force will blow it apart, overcoming the gravitational attraction?
The only thing I can think of, if the Big Bang hypothesis is to be believed, is that the Laws of Nature must somehow have been in flux initially. That's probably why we can't say for sure where all the stuff came from in the first place, cause there's no way to experiment with the original set of Laws.
Hmmmmmmm...

Good point Boerseun, that same question has crossed my mind on more than one occasion. If this is what is going on in our universe, maybe there was in fact not really a Big Bang, but rather at unpredictable intervals, many smaller Bangs. Taking this concept to it's limit, one might view the universe as eternal.

[coldcreation]

Originally Posted by infamous

If this is what is going on in our universe, maybe there was in fact not really a Big Bang, but rather at unpredictable intervals, many smaller Bangs. Taking this concept to it's limit, one might view the universe as eternal.

I agree..."maybe there was in fact not really a Big Bang"

..."many smaller Bangs" ...ask littleBang, maybe he (she?) knows.

To make a short story long...the boundary condition (with or without a singularity) is a place (or time) where (and when) the laws of physics break down. The Schwarzschild or Kerr presumption that black holes are hidden behind an event horizon is just as pathological, artificial, and surreal as the presupposition that airplanes and boats will disappear in the carnal voracity of the Bermuda triangle. This scientific game of hide and go-seek is the perfect glossolalic expression of the physicist’s creative ability—especially when considering its derivation as ‘sanctuary.’

I love the concept of black hole, but like Einstein, I don't swallow it...

[Chacmool]

Originally Posted by infamous

Good point Boerseun, that same question has crossed my mind on more than one occasion. If this is what is going on in our universe, maybe there was in fact not really a Big Bang, but rather at unpredictable intervals, many smaller Bangs. Taking this concept to it's limit, one might view the universe as eternal.

I agree. I'm much more comfortable with the idea of an eternal universe than one with a fixed beginning and end. But that's just because it makes sense to me, and we know the universe is filled with things that don't make sense.

[Anomalous]

What will happen to a star that is 100 times bigger and is made completely of pure Uranium.


This is my guess :
Uranium is used to extract energy. So when their atoms collide in the star there will be fusion and energy and the star will never collapse and all the atoms will be converted into energy ?

[Greg]

wow, thats a big story