black hole and heat

[spacehugo]

According to Hawking radiation a black hole, when loosing mass also increase its temperature, so the smaller it get the hotter it will be. by this I think (guess) this also means that the bigger a black hole get the colder it seems to be. hence this, can black holes be so big that not even heat can escape ?

 

[michaelmozina]

Theoretically speaking *all* black holes (even the small ones) are technically incapable of releasing heat (form of photons) because no photons can ever escape a black hole. The idea is that once anything passes into the event horizon, it's gone. It's a one way trip *into* the BH, and nothing (save perhaps Hawking radiation) can ever escape the event horizon.

 

[Saiph]

Your general idea is right, but your ending conclusion is wrong. No black hole, if hawking radiation exists, will ever be so large that it won't radiate. They can be very large, and radiate very, very little, but the amount is never zero.

 

[xXTheOneRavenXx]

I would have to assume then, if Hawking Radiation exists then the larger the black hole the more it will radiate then. It would have to, regardless of how minute the amount. More surface are of the BH, etc....

 

[Saiph]

other way around Raven, despite how illogical it seems.

The reason is the mechanism for radiation depends upon how steep the gravity well is near the event horizon. Big BH's have a lot of gravity, but it's spread over a much larger volume. This means that the difference in gravity just above, and just below the event horizon is small.

A small BH packs it's massive amount of gravity into a smaller volume, creating a much more drastic change in gravity just above, and below the event horizon.

Since the mechanism involves the capturing of virtual particles (only one of pair), and not your standard radiation of atoms/photons, it's this tidal force that matters. And Big BH's have weaker tidal forces, thus weaker radiation.

 

[xXTheOneRavenXx]

Ah, I see. I was actually watching a history channel episode that seemed to actually be a lot more realistic then their previous ones. But what you say does make a lot of sense in that perspective.

 

[kg]

According to Hawking radiation a black hole, when loosing mass also increase its temperature, so the smaller it get the hotter it will be. by this I think (guess) this also means that the bigger a black hole get the colder it seems to be. hence this, can black holes be so big that not even heat can escape ?

I'm not sure that Hawking radiation has even been proven but I think it is a surface to volume type of thing.

http://en.wikipedia.org/wiki/Hawking_radiation
" The radiation is as if it is emitted by a black body with a temperature that is inversely proportional to the black hole's mass."


As the black hole shrinks it looses mass to Hawking radiation faster and faster untill it finnaly pops out of existance in a flash of gamma rays. But a black hole will emit Hawking radiation no matter how big it is. You're kind of asking something like "could you make a snow ball so large that it wouldn't melt if you tossed it into the sun?".

 

[xXTheOneRavenXx]

Well, technically the existence of black holes hasn't even been "proven" per say. What affects are on surrounding bodies are believed to be caused by the presumed existence of black holes. Though there is a huge amount of suggestive affects that can so far only be explained by the existence of a black hole, a black hole can not be seen. So how can Hawking Radiation actually be "proven". I do believe in the existence of black holes based upon the affects on surrounding bodies, and Hawkings Radiation would suggest nothing remains forever in space, not even a black hole. Hawking is a very intelligent man, I would not doubt his brilliance.