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Chief Engineer Scott
2001-Nov-05, 01:14 PM
Watched an episode of Roswell High with my children yesterday, this caused great hilarity when I started ranting and raving at one point, I can't remember the full dialogue, but they had a science teacher explaining that :-
"A black hole is created when a Red Giant star goes supernova, the remnants implode to form a black hole."

Donnie B.
2001-Nov-05, 02:13 PM
Um, IIRC, this is indeed one mechanism for generating a black hole. The star has to be very, very massive; if it's just very massive, you get a neutron star instead.

The Bad Physicist
2001-Nov-20, 05:10 AM
That is true. The star needs to be at least three (this is an approximation) solar masses to become a black hole. Anything less would result in a neutron start or white dwarf. (Our star, a G2 spectral type I believe, will end up as a white dwarf.) After an explosion of a supernova, a smaller, super-dense core may be left behind. If the original star was more than three solar masses then nothing can stop its collapse and we get a black hole.

There are super-massive black holes probably at the center galaxies. These may be millions of solar masses. My area is not astrophysics, but I recall that possibly, black holes in the billions of solar masses are the driving force behind quasars. They shootout high energy jets perpendicular to their plane.

Of course, Stephen Hawking proposed a theory that predicts the existence of so-called mini black holes. These would have been created only at the beginning the universe. One bizarre implication is that these mini black holes will eventually radiate themselves out of existence after trillions of years.

jkmccrann
2005-Oct-25, 07:53 AM
Radiate themselves out of existence? But what about the Big Crunch? In any case, in trillions of years, if there is no Big Crunch, then won't the universe be so spread out that everything is basically irrelevant anyhow?

Isn't that due to the half-life of the protons out there, a few tens of billions of years or something?

mid
2005-Oct-26, 09:21 AM
No, Hawking proposed "Hawking radiation" as it's known.

It's all a bit of a mist having done this many years ago and forgot it, but it goes something like this: thanks to the wonders of quantum physics, particle-antiparticle pairs pop into existence before promptly annihilating themselves again to conserve the overall energy. Hawking suggested that this can happen on the event horizon, causing one half to be sucked away into it, 'borrowing' the energy from the black hole until it has radiated away to nothingness.