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megrfl
2008-Nov-10, 02:58 AM
A black hole sucks in matter, or anything that comes close to the event horizon, correct? Does that fact change E = mc squared, or are the "contents" of a black hole still considered a part of the universe?


While general relativity describes a black hole as a region of empty space with a point-like singularity at the center and an event horizon at the outer edge, the description changes when the effects of quantum mechanics are taken into account. Research on this subject indicates that, rather than holding captured matter forever, black holes may slowly leak a form of thermal energy called Hawking radiation and may well have a finite life.[8][9][10] However, the final, correct description of black holes, requiring a theory of quantum gravity, is unknown.

Quoted from: http://en.wikipedia.org/wiki/Black_hole

Is the above quote accurate?

spratleyj
2008-Nov-10, 03:18 AM
A black hole sucks in matter, or anything that comes close to the event horizon, correct? Does that fact change E = mc squared, or are the "contents" of a black hole still considered a part of the universe?



Quoted from: http://en.wikipedia.org/wiki/Black_hole

Is the above quote accurate?


Yes, that wiki quote is accurate... You might want to read about the information paradox, an excellent book is Susskind's The Black Hole War.
Matter doesn't just leave the universe, and black holes do evaporate via Hawking Radiation.

DrRocket
2008-Nov-10, 06:58 AM
A black hole sucks in matter, or anything that comes close to the event horizon, correct? Does that fact change E = mc squared, or are the "contents" of a black hole still considered a part of the universe?



Quoted from: http://en.wikipedia.org/wiki/Black_hole

Is the above quote accurate?

Black holes don't "suck" anything. They have a gravitational field, as does anything possessing mass. The black hole simply has a very high mass density and a gravitational field that is sufficiently strong, near the singularity, that light (and everything else) cannot escape once it is inside the event horizon. External to the event horizon the gravitational field is rather ordinary, and objects can orbit the blackhole without being sucked in. A black hole is not a vacuum cleaner. We on Earth are in all likelihood in orbit about a black hole in the center of our galaxy.

Jeff Root
2008-Nov-10, 07:37 AM
Objects can orbit beyond a distance of 3 Schwarzschild radii. Inside that
distance, everything gets pulled in, as though it were being sucked. To
maintain an orbit between the event horizon at R and the last stable orbit
at 3R requires some kind of propulsion with the exhust directed downward
toward the black hole. The closer you get to the black hole, the more
thrust you need and the less effective your engine becomes at providing
that thrust. So if you miscalculate and go the slightest bit beyond the
capability of your engines, YOU WILL BE SUCKED IN!!!!

-- Jeff, in Minneapolis

megrfl
2008-Nov-10, 02:28 PM
Super massive black holes at the center of most galaxies; pull via gravitational pull... matter, light, radiation.

http://en.wikipedia.org/wiki/Black_hole#Formation_and_evolution


A black hole is a theoretical region of space in which the gravitational field is so powerful that nothing, not even electromagnetic radiation (e.g. visible light), can escape its pull after having fallen past its event horizon.

Why is it a theoretical region? I thought that super massive black holes have been observed via light/energy "release". In addition, a mass also was observed "orbiting an event horizon".


Objects can orbit beyond a distance of 3 Schwarzschild radii.

Eventually, it is theorized based on Hawkings Radiation that black holes will dissipate (black hole evaporation).

That takes care of the E=mc squared question.

http://en.wikipedia.org/wiki/Hawking_radiation

PraedSt
2008-Nov-10, 03:08 PM
Why is it a theoretical region? I thought that super massive black holes have been observed via light/energy "release". In addition, a mass also was observed "orbiting an event horizon".

I know next to nothing about black holes, but I'll give it a go. It's probably described as 'theoretical' because all observations have been (necessarily) indirect. Hawking radiation has not yet been observed.
Also, as you/wiki quoted, 'the final, correct description of black holes, requiring a theory of quantum gravity, is unknown'.
Someone more knowledgeable will be able to give you a much better answer, I'm sure. :)

Jeff Root
2008-Nov-10, 04:09 PM
Black holes were predicted from general relativity decades before the first
evidence for their existence began to be interpreted as such. And they
were predicted from Newtonian gravity in 1783! Black holes have a long
history as theoretical objects, with only a brief history of observational
evidence for them, as yet. All of which of course is indirect.

-- Jeff, in Minneapolis

John Mendenhall
2008-Nov-10, 04:52 PM
Black holes were predicted from general relativity decades before the first
evidence for their existence began to be interpreted as such. And they
were predicted from Newtonian gravity in 1783! Black holes have a long
history as theoretical objects, with only a brief history of observational
evidence for them, as yet. All of which of course is indirect.

-- Jeff, in Minneapolis

A little more direct?

http://www.universetoday.com/2008/09/03/astronomers-link-telescopes-to-zoom-in-on-milky-ways-black-hole/

I didn't expect to see an image like this in my lifetime.

Regards, John M.

Jeff Root
2008-Nov-10, 05:44 PM
The article isn't at all clear whether the bright colored area in that first
image is constructed from actual radio data of Sagittarius A* or is just
a simulation of the same kind of thing.

-- Jeff, in Minneapolis

PraedSt
2008-Nov-10, 05:54 PM
Yeah, I thought it was a simulation.

DrRocket
2008-Nov-10, 08:15 PM
Objects can orbit beyond a distance of 3 Schwarzschild radii. Inside that
distance, everything gets pulled in, as though it were being sucked. To
maintain an orbit between the event horizon at R and the last stable orbit
at 3R requires some kind of propulsion with the exhust directed downward
toward the black hole. The closer you get to the black hole, the more
thrust you need and the less effective your engine becomes at providing
that thrust. So if you miscalculate and go the slightest bit beyond the
capability of your engines, YOU WILL BE SUCKED IN!!!!

-- Jeff, in Minneapolis

I don't think that is correct. Please provide the details or a reference supporting your assertion. Are you including some sort of consideration for gravitational radiation in your assertion ? Is that is the case, what stable orbits would exist around anything ?
http://en.wikipedia.org/wiki/Black_hole
http://en.wikipedia.org/wiki/Gravitational_radiation

mugaliens
2008-Nov-10, 09:13 PM
A little more direct?

http://www.universetoday.com/2008/09/03/astronomers-link-telescopes-to-zoom-in-on-milky-ways-black-hole/

I didn't expect to see an image like this in my lifetime.

Regards, John M.

Really? The technique has been around for a long time, albeit usuall with various co-located arrays, rather than linking up distance radio telescopes.

And it's not like we haven't been discussing this (http://www.bautforum.com/archive/index.php/t-65582.html)and similar techniques (http://www.bautforum.com/archive/index.php/t-65010.html)here on the board!