Blackholes

[All Seeing Eye]

Does the matter that enters a blackhole get released as Hawkings radiation or is that something else entirely?
If blackholes supposedly evaporate away due to the hawkings radiation where does all the matter that got sucked in go?

 

[c0rnedfr0g]

the matter is converted to energy

 

[All Seeing Eye]

the matter is converted to energy

and released as hawking radiation?

 

[rramarr]

then the blackhole dissipates.

 

[Robert Maxwell]

Yep. Matter enters. Hawking radiation comes out. Sooner or later, the black hole has "evaporated" completely.

 

[All Seeing Eye]

Is the super massive blackhole at the centre of the Milky Way giving off hawking radiation? in the billions of years it's been there why hasn't it evaporated?

 

[Argus Skyhawk]

Is the super massive blackhole at the centre of the Milky Way giving off hawking radiation? in the billions of years it's been there why hasn't it evaporated?

Yes, it is.

I would imagine it hasn't evaporated yet partly because it is so mind-bogglingly huge. Others can correct me if I'm mistaken, but I also would not be surprised if matter and energy are falling into it faster than Hawking radiation is dissipating it.

 

[Verteron]

Is the super massive blackhole at the centre of the Milky Way giving off hawking radiation? in the billions of years it's been there why hasn't it evaporated?

Yes, it is.

I would imagine it hasn't evaporated yet partly because it is so mind-bogglingly huge. Others can correct me if I'm mistaken, but I also would not be surprised if matter and energy are falling into it faster than Hawking radiation is dissipating it.

Try an experiment.

Build a quantum singularity in your bath tub using nothing but a bunch of atoms and a garlic press.

Then throw some household trash at it and see whether said trash causes the emission of hawking radiation.

Be sure to dispose of your singularity safely afterwards and keep your hands and eyes clear of the event horizon.

(Sorry I'm only teasing )

 

[PurpleBuddha]

...in the billions of years it's been there why hasn't it evaporated?

This is why:

However, the timescale for this is extremely long: a black hole of the mass of the Sun will take more than a billion times a billion times a billion times a billion times a billion times a billion times the age of the universe to evaporate completely! So it is not a process which has any significant effect for the black holes we find in astrophysical situations.

http://curious.astro.cornell.edu/question.php?number=163

When everything else (aside from other black holes) in the universe has died out and is gone, the black hole that is now at the center of the Milky Way will still exist.

 

[Asbo Zaprudder]

As I understand it, the evaporation time goes as the mass cubed (M^3). However, for a black hole to evaporate completely, it must also have an effective temperature that is greater than the black-body temperature of the background radiation (currently 2.7K). The effective temperature of the Hawking radiation varies as 1/M, so larger mass black holes have a lower temperature than small mass ones. If a black hole has the same temperature as the background radiation, it will be in equilibrium with it. The effect is that black holes whose mass is greater than about 1% of the Earth's mass cannot currently evaporate (although I guess they would if you placed them in a refrigerated adiabatic enclosure).

I understand that the question as to whether information that falls into a black hole is lost forever to the Universe is still somewhat moot -- Hawkings recently his position a few years back to favour the opinion that the information is preserved in some fashion -- perhaps as perturbations in the Hawking radiation, by being shunted to parallel universes.

 

[PurpleBuddha]

^

That sounds about right, the lifetime of a black hole is currently said to be proportional to the cube of its mass.

And about absorbing:

As an example, a black hole of one solar mass has a temperature of only 60 nanokelvin; in fact, such a black hole would absorb far more cosmic microwave background radiation than it emits. A black hole of 4.5 × 1022 kg (about the mass of the Moon) would be in equilibrium at 2.7 kelvin, absorbing as much radiation as it emits. Yet smaller primordial black holes would emit more than they absorb, and thereby lose mass.

Correct me if I am wrong here, but even a the larger black holes should eventually run out of food as the universe expands and once it has nothing to feed on then any evaporation rate, no matter how slow, will mean that it should eventually evaporate completely.

 

[Asbo Zaprudder]

Correct me if I am wrong here, but even a the larger black holes should eventually run out of food as the universe expands and once it has nothing to feed on then any evaporation rate, no matter how slow, will mean that it should eventually evaporate completely.

That's my understanding as well.

 

[scotthm]

Correct me if I am wrong here, but even a the larger black holes should eventually run out of food as the universe expands and once it has nothing to feed on then any evaporation rate, no matter how slow, will mean that it should eventually evaporate completely.

Why can't it re-feed on the matter once it evaporates? Wouldn't such matter be sitting just outside the event horizon, waiting to be swallowed up again?

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[Asbo Zaprudder]

Correct me if I am wrong here, but even a the larger black holes should eventually run out of food as the universe expands and once it has nothing to feed on then any evaporation rate, no matter how slow, will mean that it should eventually evaporate completely.

Why can't it re-feed on the matter once it evaporates? Wouldn't such matter be sitting just outside the event horizon, waiting to be swallowed up again?

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If I remember this correctly, the evaporation process takes place via pair production of particles and antiparticles from the vacuum -- one particle drops into the black hole, and one escapes to infinity by quantum tunnelling. I guess this implies that the proportion of antimatter to matter should increase over vast aeons of time to 50% from the initial significant imbalance at the Big Bang.

 

[Icemizer]

Tachyon the answer to your question is no one has a clue, its all guess work including the very existence of black holes(stupid name for a gravity ball anyway). But if you want some info this site should help you out.

http://imagine.gsfc.nasa.gov/docs/ask_astro/black_holes.html

 

[Asbo Zaprudder]

Tachyon the answer to your question is no one has a clue, its all guess work including the very existence of black holes(stupid name for a gravity ball anyway). But if you want some info this site should help you out.

http://imagine.gsfc.nasa.gov/docs/ask_astro/black_holes.html

I tend to agree, although the guessers are very smart people so I wouldn't dismiss the theories too readily. My own opinion is that we just don't know enough about what happens to space-time and mass-energy under the extreme conditions that are being described. Alternate theories, such as gravistars and dark energy stars, don't held up as well to scrutiny as the now more traditional black hole theory. My guess is that the vacuum undergoes a phase change to a higher energy state rather than a singularity forming, but I'm just blowing gas here.

 

[PurpleBuddha]

Tachyon the answer to your question is no one has a clue, its all guess work including the very existence of black holes(stupid name for a gravity ball anyway). But if you want some info this site should help you out.

http://imagine.gsfc.nasa.gov/docs/ask_astro/black_holes.html

It goes a long way beyond the type of guessing that involves flipping a coin.


Particularly when we are talking about the existence of black holes themselves:

http://library.thinkquest.org/10148/long16.shtml

http://library.thinkquest.org/10148/bh_94.shtml

And sure, some of the theoretical constructs could be wrong. But if they are, my bet is they are wrong more in the sense that Newton was wrong (he was on to something, just missing a few important details). Yes, there is the possiblity that Hawking is completely wrong, but learning and expanding is the nature of science and is what makes it great.

 

[Argus Skyhawk]

Try an experiment.

Build a quantum singularity in your bath tub using nothing but a bunch of atoms and a garlic press.

Then throw some household trash at it and see whether said trash causes the emission of hawking radiation.

Great. Now my bathtub and my garlic press are missing, and there is a hole in the floor where the quantum singularity fell into the Earth.

 

[Asbo Zaprudder]

Actually, some researchers at St Andrews Universtity have used laser light and even water to simulate event horizons in the lab:

http://www.universetoday.com/2008/02/13/synthetic-black-hole-event-horizon-created-in-uk-laboratory/

http://www.astronomyreport.com/research/Black_holes_made_of_light.asp

http://www.inthenews.co.uk/infocus/features/in-focus/watery-black-holes-$1222465.htm

They even say that it may be possible to detect an analogy for Hawking radiation from the simulated event horizons.

 

[FlyingLemons]

Does the matter that enters a blackhole get released as Hawkings radiation or is that something else entirely?
If blackholes supposedly evaporate away due to the hawkings radiation where does all the matter that got sucked in go?

This is quite a difficult question really - it's an area of current research that continues to be heavily disputed due to the fact that we don't understand how gravity works on a quantum scale. Hawking claimed to have solved the problem of matter going into a black hole, but we (i.e. physicists) aren't entirely convinced.

Basically, we draw an analogy between the laws of thermodynamics, and black holes, which allows Hawking radiation. The Hawking radiation itself comes from quantum foam (particles popping in and out of existence) near the horizon of the black hole, and then particles "steal" the energy of the hole and shoot off, becoming the famous Hawking radiation. Whether this allows information to come back out or not is vague, but from a string theory point of view the answer is "maybe", although it comes out in a garbled form.