Science Questions

Can black holes lose enough mass to stop being black holes?

Sat, 11th Aug 2012

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Mark Anderson asked:

I have a question regarding Black Holes.


Since Black holes can lose mass by Hawking Radiation, is it possible for them to lose sufficient mass to no longer be a Black Hole, and become, say, a Neutron Star?


Mark Anderson

Windsor, Ontario, Canada




Dominic -   There is a process by which black holes can lose mass and what happens is that over time, in the vacuum of space, there's a quantum process by which particles and anti-particles are popping out of the vacuum of space.  If one of those two particles, the anti-particle, falls into the black hole and the other particle, the real mass particle, does not fall into the black hole then you’ve got a particle out of the black hole.  The anti-particle has fallen in and will annihilate with matter inside the black hole, and that causes the black hole to lose mass.

This is a very slow process for the kinds of astrophysical black holes you see in the centres of galaxies and that form out of supernova explosions.  But if you were, for example, to take a small black hole – I did a calculation a while back for one the size of a double decker bus – then this is actually quite a fast process and a black hole the size of a double decker bus would last about 1000th of a second before it would just evaporate into the vacuum of space.  But obviously, real black holes are around about the mass of the Sun or many million times that mass and they will lose mass very slowly compared to the amount of mass they have.


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Yes. They're said to evaporate and tehn explode. Black holes can loose matter by radiating Hawking radiation. Pmb, Fri, 15th Jun 2012

The explosion at the end of life of a blackhole would only occur when its mass has dropped to one Planck unit which would be converted into radiation it would at no time convert to a Neutron star as the density has gone far past that stage. syhprum, Fri, 15th Jun 2012

Whilst I agree with Syhprum that no transition would be made via neutron stars (and any other form of degenerate matter) I don't know the reason to put a planck mass as the lower mass limit.  The energy mass equivalence of a planck mass is vast as the planck mass is the only real world sized base unit of the planck scale.  The energy given off by a planck mass converting to hawking radiation would be around half a megawatthour / a billion joules or so, the temperature would be 10^30 K, and life time about 10^6 planck times/10^-38 seconds  (sorry for the horrific mix of units) imatfaal, Sat, 16th Jun 2012

I gave an "off the top of my head" comment as is my wont and stand to be corrected, I thought the Planck mass was defined in terms of the minimum mass of a black hole.
A billion Joules aint all that much on the cosmic scale.
My supposition is supported by this article

With regards units should we not talk about  10^14 Ergs syhprum, Sat, 16th Jun 2012

Not really, it's called pair production and are presumed to happen more often the more 'energy' you get by in some specific space. A Black Holes event horizon is one such area where there should be a lot of 'energy' per cubic centimeter, and so there should be a lot of spontaneous pair productions there. They are also 'entangled' as I understands it, and when they split, one passing the event horizon the other staying outside it the idea is that the one getting in will annihilate a particle somewhere inside it and so setting the 'information' of its spin to its twin outside it. And that should be the 'information' it releases. But you do not get rid of the energy created inside that Black Hole by those two particles interacting (anti matter-matter annihilating), as far as I know?

Whether that spin, or polarization as in a photon, is all information necessary to recreate a exact replica of the matter destroyed I don't know either? Is it? And what about if the particles belonged to structure extending the information set, as writing on ice?

It's a mysterious field to me. yor_on, Wed, 15th Aug 2012

So, as far as I can tell, my question was not answered. Nobody really seems to know. It might explode, or, ........????? Mark Anderson, Wed, 15th Aug 2012

No, it can't 'transform' into matter again, not as I understands it. Although I don't know what 'energy' could exist in that confined space, as defined by us outside, as it 'shrink'. To me that energy only have one way to go and that's 'up', unless we assume that 'energy' somehow can disappear from inside that Black Hole by some other process. As far as I get it it's only 'matter' as particles that disappear inside it? But as I said, I'm not sure :) yor_on, Wed, 15th Aug 2012

Doc your short lived black hole may have as much mass as a double decker bus but it must be much smaller than an atom say around (10^-8 times the size). A black hole the SIZE of a DD bus say around 10m weighs one thousand times the mass of the earth and lasts around 10^60 years.

black holes lose almost all their energy as very low frequency radio or possibly gravitational radiation and just a tiny phut of particles near the end of their vastly long lives after they have lost almost all their mass and weigh about as much as a small asteroid the size of a mountain.  by the way their physical size at this time is about the same size as the nucleus of an atom 10^-15 m or 1 fermi Soul Surfer, Wed, 15th Aug 2012

The size of a mountain is rather a vague unit of volume, how do you define the volume of a mountain do you slice it off at ground level (in a thought experiment) but ground level may well already be 5000 m high in the case of the Himalayas or 5000 m deep in the case of Hawaii, rather puts me in mind of using blue whales or Olympic swimming pools may I suggest cubic Km syhprum, Wed, 15th Aug 2012

Actually at the center of a black hole spacetime has infinite curvature and matter is crushed to infinite density under the pull of infinite gravity. At a singularity, space and time cease to exist as we know them. The laws of physics as we know them break down at a singularity, so it's not really possible to envision something with infinite density and zero volume

that is one, among many theories.

in reality, no one knows "exactly" what happens to the matter inside of a black hole... Emc2, Thu, 16th Aug 2012

It's been on my mind for some time now. 'energy' that is. Maybe I'm wrong in assuming that whatever energy exist inside a Black Hole should stay put there? Maybe 'energy' is more of a balance, some sort of unified field for everything inside a SpaceTime, including Black Holes? One could assume that if there is a spontaneous pair production of particles at the event Horizon that this should tap 'energy' of the Black Hole too? The question seems to become what a event Horizon says to us. Light or radiation can't pass from the inside, but, what is 'energy'?

And what does a event horizon state when it comes to it (energy)? yor_on, Fri, 17th Aug 2012

I hope one day, they can send a unmanned probe into one........
just to get some readings as it passed over the event horizon, and beyond.

  maybe with an Ion engine, it could reach one in a few million years.......

  interesting : Emc2, Sat, 18th Aug 2012

No way we can get photons to 'bounce out' from inside a event horizon :)
Mini holes or someting equivalent would be cool though?
But what the he* is 'energy'? Transformations or a 'field', or both? yor_on, Mon, 20th Aug 2012

My theory is that matter gets essentially torn apart at the event horizon. I think that the event horizon necks out as each particle approaches, and this small curvature perturbation creates local Hawking radiation, and this Hawking radiation permits waves of gravity that immediately surround the black hole and this solves the information problem.

In other words I think the 'no hair' conjecture to be (effectively) false. wolfekeeper, Tue, 21st Aug 2012

  maybe the radio waves might make it, or some other medium to carry the signal, maybe quantum communication of some type...hopefully in the next 30 years or so, lol... I wanna know Emc2, Tue, 21st Aug 2012

My theory is that matter gets essentially torn apart at the event horizon. I think that the event horizon necks out as each particle approaches, and this small curvature perturbation creates local Hawking radiation, and this Hawking radiation permits waves of gravity that immediately surround the black hole and this solves the information problem.

In other words I think the 'no hair' conjecture to be (effectively) false.

  that is my like my theory, I believe that all matter in a black hole gets reduced to its elementary particles during the space time warp that mathematically occurs after the event horizon.  I also believe black holes are the recyclers of the universe, keeping a fresh supply of atoms flowing into the mix so to speak...

I also believe the universe is infinite and has always existed.....and that black holes of different types, help in keeping new matter repopulating the great expanses of infinity.. Emc2, Tue, 21st Aug 2012

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