Black Holes ain't so black...

Slick · #1 July 21st, 2004, 10:07 PM

http://www.cnn.com/2004/TECH/space/0....ap/index.html

Slick.

Renegade 13 · #2 July 22nd, 2004, 04:50 AM

Very interesting stuff. I don't quite understand though; the universe has been around for billions of years, I would think that some of the original black holes would have "deteriorated" and spit the matter back out into the universe in its new "mangled" form by now. How come we haven't detected such a massive ejection of matter into space by now? Maybe we just haven't been looking for it, or are not capable of detecting it just yet?

Slick · #3 July 22nd, 2004, 05:00 AM

I don't know the details of his newest theory, but in "A Brief History of Time", he mentions that black holes can "evaporate". This happens when a pair of "virtual" particles (one particle and one anti-particle) are created just outside the event horizon. Some of the time, only the anti-particle falls into the black hole. This then annihilates some of the matter in the black hole, thus reducing its mass, while the particle from the other half of the pair escapes and can be seen as "radiation" from the black hole. Obviously this theory has been modified or maybe even replaced by his newer one. I hope Hawking writes another book before he dies.

Slick.

Aiken · #4 July 22nd, 2004, 07:24 AM

hehe, RIP Wormholes.

Karibu · #5 July 22nd, 2004, 09:14 AM

Quote:

Originally posted by Renegade 13:
Very interesting stuff. I don't quite understand though; the universe has been around for billions of years, I would think that some of the original black holes would have "deteriorated" and spit the matter back out into the universe in its new "mangled" form by now. How come we haven't detected such a massive ejection of matter into space by now? Maybe we just haven't been looking for it, or are not capable of detecting it just yet?

The life time of black holes is billions of times as long as our universe is old by now. To make it more understandable, our universe is about 10^10 years old (10 billion years. I know it is about 5 billion years, but I speak of cosmological decades, not exact years, so 10^10 years is fitting).

In year 10^40 there are nothing but black holes and neutron stars left in our universe. Most black holes have been evaporated by year 10^67. Most massive black holes live as old as 100^100 years. After that there is nothing but radiation left. If you are interested to know more, I suggest you find a book The Five Ages of the Universe - Inside the Physics of Eternity by Fred Adams & Greg Laughling. Very captivating book.

Renegade 13 · #6 July 22nd, 2004, 04:12 PM

Quote:

Originally posted by Karibu:
The life time of black holes is billions of times as long as our universe is old by now. To make it more understandable, our universe is about 10^10 years old (10 billion years. I know it is about 5 billion years, but I speak of cosmological decades, not exact years, so 10^10 years is fitting).

I thought cosmologists had narrowed the age of the universe down to somewhere between 14 and 15 billion years old.

But perhaps I'm mistaken.

Slick · #7 July 22nd, 2004, 04:30 PM

Actually, the rate at which a black hole evaporates (under Hawking's theory) is related to its mass. The larger the black hole, the slower it evaporates. More accurately, it's related to the surface area of the event horizon (proportional to mass squared or possibly cubed, I don't have the formula in front of me).

Also, there are theories that allow for the creation of black holes by mechanisms other than stellar collapse. These other mechanisms could produce black holes of quite small mass which would have very short lifetimes relative to the age of the universe.

Slick.

[ July 22, 2004, 15:34: Message edited by: Slick ]

spoon · #8 July 22nd, 2004, 04:54 PM

Quote:

Originally posted by Slick:
Also, there are theories that allow for the creation of black holes by mechanisms other than stellar collapse.

...such as when PBW goes down...

Suicide Junkie · #9 July 22nd, 2004, 07:23 PM

Quote:

Originally posted by Slick:
Also, there are theories that allow for the creation of black holes by mechanisms other than stellar collapse. These other mechanisms could produce black holes of quite small mass which would have very short lifetimes relative to the age of the universe.

Slick.

There are also potentially "primordial black holes" which would have been generated about the time of the big bang at a variety of sizes...
As such, they'd evaporate at various times, and might be visible from the burst of radiation as they die.
Too close, and they'd irradiate the solar system killing everything, of course, so there is an upper limit as to how many could be floating around.

Slick · #10 July 22nd, 2004, 08:32 PM

Yes, that is one of the other mechanisms for creation of black holes. Not to scare anyone, but gamma ray observing satellites "see" about 1 huge gamma ray burst per day from varying, but so far safe, distances. The question of what causes these is debated. One postulated source is the "death" of a black hole. If one occurred close to our solar system, we would be fried.

Slick.