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Prometheus

What eats black holes?

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So apparently Hawking radiation happens when pairs of virtual particles are created on an event horizon and one of the pair falls into the event horizon while the other flies away, somehow taking mass with it.

If there were a way to create more such virtual particles at the event horizon, would the black hole then evaporate faster?

Are there any other vaguely realistic ways of destroying black holes?

 

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This is a 'crude' explanation of the mechanism, but it is easy to understand, and so, often used.

I would imagine the virtual particle 'flux' is related to the surface area of the event horizon.
Increase the EH surface area and you increase the virtual particles involved in the mechanism.

However, the EH surface area is also a measure of the BH's entropy, which implies it has a temperature.
Increasing the EH surface area decreases the temperature, so the peak of the black body spectrum of the emitted radiation is at a lower temperature.
For stellar size ( and above ) the emitted radiation is at very low temperatures ( so low in fact, that the 2.7 deg of the CMB increases the BH's mass faster than Hawking radiation decreases it ) is very long wavelength/low energy.
So increasing surface area increases the amount of radiation, but it is of lower energy and so, carries away much less mass/energy from the BH.
It is only BHs that have already mostly evaporated, or may be left over from the Big Bang, which produce copious amounts of gamma radiation ( Star Trek's Romulan 'bird if prey' starships use a micro BH as their power source ); just before shedding their EH and exploding back into 'normal' space-time.

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5 hours ago, Prometheus said:

So apparently Hawking radiation happens when pairs of virtual particles are created on an event horizon and one of the pair falls into the event horizon while the other flies away, somehow taking mass with it.

Simply, it is the law of conservation that is being enforced...the possibility exists that the positive escaping particle becoming real, and the virtual particle falling in is negative, thereby subtracting from the overall mass of the BH.

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On 1/20/2019 at 5:35 PM, MigL said:

This is a 'crude' explanation of the mechanism, but it is easy to understand, and so, often used.

I would imagine the virtual particle 'flux' is related to the surface area of the event horizon.
Increase the EH surface area and you increase the virtual particles involved in the mechanism.

However, the EH surface area is also a measure of the BH's entropy, which implies it has a temperature.
Increasing the EH surface area decreases the temperature, so the peak of the black body spectrum of the emitted radiation is at a lower temperature.
For stellar size ( and above ) the emitted radiation is at very low temperatures ( so low in fact, that the 2.7 deg of the CMB increases the BH's mass faster than Hawking radiation decreases it ) is very long wavelength/low energy.
 

The only way of increasing the EH surface area would be to increase its mass though, isn't it?

Isn't it the case that the more massive BH, and hence larger EH surface area, the more slowly it evaporates, implying something else is at play?

 

On 1/20/2019 at 6:47 PM, beecee said:

Simply, it is the law of conservation that is being enforced...the possibility exists that the positive escaping particle becoming real, and the virtual particle falling in is negative, thereby subtracting from the overall mass of the BH.

 

So these virtual particles pairs have to obey conservation laws - is it a mass/energy conservation?

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Correct on both counts.

Increasing mass/energy of the BH increases surface area of the EH, and the 'temperature' decreases. This is strictly from entropy consideration.
Virtual particles exist on 'borrowed' energy, once their time is up, the energy has to be repaid. The universe is a strict lender, if it can't get its energy back from the virtual particles anymore, it takes it from the BH responsible.

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One further detail, if the surrounding blackbody temperature outside the BH is hotter than the blackbody temperature of the EH. Then the BH will gain mass. This lends itself to the rate a BH will lose mass, as a smaller EH surface area is hotter it will lose at a rate faster rate with a given surrounding blackbody temperature. CMB temperature today being 2.73 Kelvin it would be highly unlikely any BH larger than the mass of the moon if memory serves correct on the calculations will radiate Hawking radiation at todays CMB temperature. Going from memory on the BH mass, so might be a bit off.

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Well then it seems that time is the only thing that eats black holes, and lots of it. Is the CMB temperature falling? If so this could speed up BH evaporation - but still at cosmic timescales i guess.

Anyway, i'm writing a sci-fi short so i'm just going to have the scientists create virtual particles at the event horizon to attempt to evaporate it more quickly. It's going to go wrong and end with a gamma ray burst that sterilises life for a wide sweep of the galaxy.

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11 minutes ago, Prometheus said:

Well then it seems that time is the only thing that eats black holes

Profound, depressing and also slightly cheering!

12 minutes ago, Prometheus said:

Is the CMB temperature falling? If so this could speed up BH evaporation - but still at cosmic timescales i guess.

Yes, and yes!

13 minutes ago, Prometheus said:

It's going to go wrong and end with a gamma ray burst that sterilises life for a wide sweep of the galaxy.

Could be worse, then.

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30 minutes ago, Prometheus said:

...It's going to go wrong and end with a gamma ray burst that sterilises life for a wide sweep of the galaxy.

You could leave out an exotic energy based life form that feeds on gamma rays and thrives because of the event :) 

Nice post @MigL, I learned some. 

Edited by koti

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Damn, Prometheus.
I was going to read your short story.
But now you've spoiled it by giving away th ending.
 

Thanks Koti.

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Well i might change the ending in light of koti's suggestion: put a slither of silver in the lining at least.

When black holes are very small, they're very hot. But do they actually emit gamma rays? I couldn't find much information about what happens to a black hole in its death throes. 

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As they 'evaporate', and increase in temperature, they emit more and more energetic particles.
These carry more and more mass-energy away at faster and faster rates.
Eventually the micro ( by now ) BH, loses enough mass-energy that it can shed its event horizon.
At this point it 'explodes' back into normal space-time with a massive gamma ray burst.

This scenario, though, involves the 'loss of information', which is a paradox according to QM.
This might explain why we've never seen gamma bursts from evaporating primordial BHs, left over from the Big Bang.
( maybe it just doesn't happen in this manner )

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11 hours ago, MigL said:

As they 'evaporate', and increase in temperature, they emit more and more energetic particles.
These carry more and more mass-energy away at faster and faster rates.
Eventually the micro ( by now ) BH, loses enough mass-energy that it can shed its event horizon.
At this point it 'explodes' back into normal space-time with a massive gamma ray burst.

 

well answered +1

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If you want to play around with the properties of black holes, there is a useful calculator here: http://xaonon.dyndns.org/hawking/

You can put in one value (mass, radius, temperature, etc) and it will calculate all the others.

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