Can a black hole exist at absolute zero K? Is there a minimum temperature required for a black hole to exist? You would think that making something cold enough would stop it spinning.

There are several types of black holes: Schwarzschild, Reissner-Nordstrom, Kerr, Kerr-Newman. All have mass, some also electric charge, some mass and angular momentum. The Kerr-Newman type has mass, charge and angular momentum. I am getting this info from an article by prof.Remo Ruffini of Rome University which I translated in 1972 from English. So not all of them are spinning.
Tullio

All our assumptions about black holes assume that they always are spinning.

Are there, or can there be, any black holes that are not rotating?You can have non-spinning black holes.

They are just less likely to form than rotating ones. To be absolutely non-rotating the infalling of matter to produce it must be ( nett ) purely radial. To risk mild confusion in this discussion, in the case of rotation the surface for which light is trapped is different ( except at the poles of rotation ) from the surface at which material bodies are doomed. So there are effectively two horizons ..... but I don't think that is of especial consequence for our discussion here.

Quote:

Are 'black holes' in effect a perpetual energy machine?

There's no breach of conservation of energy. In a way black holes store it for later on, deferring energy release ( back into the remainder of universe ) to the way distant future - something like 10^60 years or somesuch. By then a black hole of any conceivable size ought evaporate per Hawking radiation. As the event horizon masks the presence of whatever is at a black hole's centre then from the point of view of the rest of the universe the energy budget is square.

Having said that it is a big bucket of energy, from which rotational energy may be harvested. In one scenario, if a Dyson Sphere is constructed around a black hole one can shoot material inwards on certain trajectories, to graze oblivion and thence return with more kinetic energy than it left. The black hole loses angular momentum appropriately. This is already true for non-relativistic cases, and has been used many times for our space probes exploring the outer solar system particularly. One can rob the Sun and various planets of what is for them a smidgen of their total angular/orbital momentum to achieve paths we would have no practical hope of attaining if we relied purely upon fuel carried at launch.

Mind you it is worth emphasising that energy conservation is a self fulfilling calculational construct. The history of the concept is to add new forms of energy if some loss/gain is unaccounted for. It is an incredibly useful generalisation however. What energy actually 'is' remains moot.

Quote:

.... assuming a 'singularity' with infinities of density and gravitation ...

This is one of the annoying aspects to thinking about black holes - from where/when are you describing it? We don't sweat it if two disparate descriptions don't agree when there is no mechanism to compare histories. If you stay distant the event horizon is your limit of information. If you go in you never come back ....

Quote:

Can a black hole exist at absolute zero K? Is there a minimum temperature required for a black hole to exist? You would think that making something cold enough would stop it spinning.

Terrific question! This is a way deeper issue than you might at first think ....

Since a lower black hole temperature comes from a larger one, then in the limit of infinite mass/size the temperature ought approach zero. But what is then left of the remainder of the universe to observe that external to the hole? But it is still anti-intuitive because a cooler black hole ought absorb energy from a hotter surrounding ( heat bath ). Even the CMB radiation at a few degrees Kelvin may be warmer than a black hole within it! What then?

Here's a thing. One line of thinking I've read posits that an event horizon represents a single microstate :

If one considers classical thermodynamics the idea of entropy relies upon a given macroscopic variable ( like total system energy ) being consistent with numerous but actually distinct internal states of the system. These all have some specific total energy, say, but we aren't tracking the microscopic detail for each. This is like saying that a bridge hand is 'strong in Hearts', which substantially narrows the field from all possible deal permutations, but still leaves open the exact composition of the cards one holds. It's not simply a measure of disorder but one of ignorance too. One definition of entropy looks at how the number of microstates changes with the total system energy and temperature. For a black hole you can chuck in massive amounts of mass/energy and barely change the externally measured temperature. The negative specific heat mentioned earlier expresses the behaviour that the direction of the temperature change is down as the mass goes up.

Now a single monolithic microstate as a description of a black hole ( from afar ) is essentially saying it is one bloody huge particle with no internals to discriminate! It only outwardly shows mass, angular momentum and electric charge. Oddly enough many 'fundamental' particles have exactly that as their model too. But here we understand them ( or think we do ) in quantum mechanical terms. By analogy does this mean ( here's the punch line ) that a black hole should have a minimum spin value?

For my money : an explanation which adequately encompasses this black-hole/fundamental-particle duality is where the melding of gravity with QM lies.

At a deeper level what we are discovering is the limit of the extension of our principles/rules/laws/knowledge from here-abouts and now-abouts to way away parts of spacetime. In the absence of harder data - which has to be delivered to Earth for us to decide, by the way - it isn't known what will remain true and what may be approximate/malleable. So I've tried to indicate from my understanding what it is we conceptually rely upon to reach a given conclusion. Humility ( or a principle of mediocrity ) puts us at a disadvantage data wise. Any close up examination of the many of the things we speak of exclude our very survival, hence with LIGO/LISA etc we seek 'distant echoes' ......

I'd probably better ease up here, as I'm driving Martin ever closer to drink! Asymptotic Vodka* anyone? :-)

Cheers, Mike.

( edit ) * - this is related to Absolut Vodka. It's nearly, but not quite, the same ...... :-)

( edit ) Running further along the black-hole/fundamental-particle duality/analogy path. Does a black hole conserve stuff like baryon number, lepton number, weak isospin, strong hypercharge and all that sort of quantum numerology that you'd discuss at a particle collider? How would you know either way? For that matter, would anyone like to quote the Earth's baryon number? Is it odd or even? Is it prime? Did it change from yesterday? Last year? In reality do the numbers with great predictive merit at small scales ( low counts ) survive as truly measurable quantities in the large extremes? When an electron in a hydrogen atom increases it's energy it will step up the rungs of the quantum ladder ( a result of confining a wave ie. resonance ), so that the step ups will become progressively smaller as it approaches freedom/ionisation. Is there a photon with a wavelength sufficiently long, or of a frequency sufficiently low ( in a universe of finite extent and/or finite age ) to represent any arbitrarily small energy jump?

I have made this letter longer than usual because I lack the time to make it shorter.Blaise Pascal

Astronomers using NASA's Chandra X-ray Observatory have found evidence of the youngest black hole known to exist in our cosmic neighborhood. The 30-year-old black hole provides a unique opportunity to watch this type of object develop from infancy...

Keep searchin',
Martin

(At present rates, I'm 'busy' until Christmas before any more relativistic searching :-( )

Astronomers using NASA's Chandra X-ray Observatory have found evidence of the youngest black hole known to exist in our cosmic neighborhood. The 30-year-old black hole provides a unique opportunity to watch this type of object develop from infancy...

Keep searchin',
Martin

(At present rates, I'm 'busy' until Christmas before any more relativistic searching :-( )

Good find Martin! :-)

What a fascinating object, with such a known timeline of evolution. I'm waiting for the smoke to clear on SN1987A .....

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter.Blaise Pascal

## Can a black hole exist at

)

Can a black hole exist at absolute zero K? Is there a minimum temperature required for a black hole to exist? You would think that making something cold enough would stop it spinning.

## There are several types of

)

There are several types of black holes: Schwarzschild, Reissner-Nordstrom, Kerr, Kerr-Newman. All have mass, some also electric charge, some mass and angular momentum. The Kerr-Newman type has mass, charge and angular momentum. I am getting this info from an article by prof.Remo Ruffini of Rome University which I translated in 1972 from English. So not all of them are spinning.

Tullio

## RE: All our assumptions

)

They are just less likely to form than rotating ones. To be absolutely non-rotating the infalling of matter to produce it must be ( nett ) purely radial. To risk mild confusion in this discussion, in the case of rotation the surface for which light is trapped is different ( except at the poles of rotation ) from the surface at which material bodies are doomed. So there are effectively two horizons ..... but I don't think that is of especial consequence for our discussion here.

There's no breach of conservation of energy. In a way black holes store it for later on, deferring energy release ( back into the remainder of universe ) to the way distant future - something like 10^60 years or somesuch. By then a black hole of any conceivable size ought evaporate per Hawking radiation. As the event horizon masks the presence of whatever is at a black hole's centre then from the point of view of the rest of the universe the energy budget is square.

Having said that it is a big bucket of energy, from which rotational energy may be harvested. In one scenario, if a Dyson Sphere is constructed around a black hole one can shoot material inwards on certain trajectories, to graze oblivion and thence return with more kinetic energy than it left. The black hole loses angular momentum appropriately. This is already true for non-relativistic cases, and has been used many times for our space probes exploring the outer solar system particularly. One can rob the Sun and various planets of what is for them a smidgen of their total angular/orbital momentum to achieve paths we would have no practical hope of attaining if we relied purely upon fuel carried at launch.

Mind you it is worth emphasising that energy conservation is a self fulfilling calculational construct. The history of the concept is to add new forms of energy if some loss/gain is unaccounted for. It is an incredibly useful generalisation however. What energy actually 'is' remains moot.

This is one of the annoying aspects to thinking about black holes - from where/when are you describing it? We don't sweat it if two disparate descriptions don't agree when there is no mechanism to compare histories. If you stay distant the event horizon is your limit of information. If you go in you never come back ....

Terrific question! This is a way deeper issue than you might at first think ....

Since a lower black hole temperature comes from a larger one, then in the limit of infinite mass/size the temperature ought approach zero. But what is then left of the remainder of the universe to observe that external to the hole? But it is still anti-intuitive because a cooler black hole ought absorb energy from a hotter surrounding ( heat bath ). Even the CMB radiation at a few degrees Kelvin may be warmer than a black hole within it! What then?

Here's a thing. One line of thinking I've read posits that an event horizon represents a single microstate :

If one considers classical thermodynamics the idea of entropy relies upon a given macroscopic variable ( like total system energy ) being consistent with numerous but actually distinct internal states of the system. These all have some specific total energy, say, but we aren't tracking the microscopic detail for each. This is like saying that a bridge hand is 'strong in Hearts', which substantially narrows the field from all possible deal permutations, but still leaves open the exact composition of the cards one holds. It's not simply a measure of disorder but one of ignorance too. One definition of entropy looks at how the number of microstates changes with the total system energy and temperature. For a black hole you can chuck in massive amounts of mass/energy and barely change the externally measured temperature. The negative specific heat mentioned earlier expresses the behaviour that the direction of the temperature change is down as the mass goes up.

Now a single monolithic microstate as a description of a black hole ( from afar ) is essentially saying it is one bloody huge particle with no internals to discriminate! It only outwardly shows mass, angular momentum and electric charge. Oddly enough many 'fundamental' particles have exactly that as their model too. But here we understand them ( or think we do ) in quantum mechanical terms. By analogy does this mean ( here's the punch line ) that a black hole should have a minimum spin value?

For my money : an explanation which adequately encompasses this black-hole/fundamental-particle duality is where the melding of gravity with QM lies.

At a deeper level what we are discovering is the limit of the extension of our principles/rules/laws/knowledge from here-abouts and now-abouts to way away parts of spacetime. In the absence of harder data - which has to be delivered to Earth for us to decide, by the way - it isn't known what will remain true and what may be approximate/malleable. So I've tried to indicate from my understanding what it is we conceptually rely upon to reach a given conclusion. Humility ( or a principle of mediocrity ) puts us at a disadvantage data wise. Any close up examination of the many of the things we speak of exclude our very survival, hence with LIGO/LISA etc we seek 'distant echoes' ......

I'd probably better ease up here, as I'm driving Martin ever closer to drink! Asymptotic Vodka* anyone? :-)

Cheers, Mike.

( edit ) * - this is related to Absolut Vodka. It's nearly, but not quite, the same ...... :-)

( edit ) Running further along the black-hole/fundamental-particle duality/analogy path. Does a black hole conserve stuff like baryon number, lepton number, weak isospin, strong hypercharge and all that sort of quantum numerology that you'd discuss at a particle collider? How would you know either way? For that matter, would anyone like to quote the Earth's baryon number? Is it odd or even? Is it prime? Did it change from yesterday? Last year? In reality do the numbers with great predictive merit at small scales ( low counts ) survive as truly measurable quantities in the large extremes? When an electron in a hydrogen atom increases it's energy it will step up the rungs of the quantum ladder ( a result of confining a wave ie. resonance ), so that the step ups will become progressively smaller as it approaches freedom/ionisation. Is there a photon with a wavelength sufficiently long, or of a frequency sufficiently low ( in a universe of finite extent and/or finite age ) to represent any arbitrarily small energy jump?

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## We've got a real young one to

)

We've got a real young one to look at for real:

NASA's Chandra Finds Youngest Nearby Black Hole

Astronomers using NASA's Chandra X-ray Observatory have found evidence of the youngest black hole known to exist in our cosmic neighborhood. The 30-year-old black hole provides a unique opportunity to watch this type of object develop from infancy...

Keep searchin',

Martin

(At present rates, I'm 'busy' until Christmas before any more relativistic searching :-( )

See new freedom: Mageia Linux

Take a look for yourself: Linux Format

The Future is what We all make IT (GPLv3)

## RE: We've got a real young

)

Good find Martin! :-)

What a fascinating object, with such a known timeline of evolution. I'm waiting for the smoke to clear on SN1987A .....

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## RE: What a fascinating

)

I could mail you a pdf copy of the following article:

SN1987A: Revisiting the Data and the

Correlation between Neutrino and

Gravitational Detectors

by P.Galeotti, G.V.Pallottino & G.Pizzella

October 21 2008

arXiv:0810.3759v1 [gr-qc]

But I should need your mail address.

Tullio