The Entropy of Black Holes: Evidence and Implications

[Felgar]

Just found the forum today, looks like a great community. :) Anyways, one thing I've always wondered since my university days and my Intoduction to Astronomy course... :)

One thing I've always wondered is what evidence we have that a black hole is actually a singularity where its matter no longer exists... Consider:

We have a normal sun where atoms are mostly free and under fairly low pressure. If a star is big enough it will collapse to a neutron star, where basically the force of gravity is enough to collapse the area of an atom down to a nuclear level... So that whatever forces maintain the normal electron field around an atom are overcome and we basically get a star that amounts to one giant nucleus made up of many neutrons. I think I'm right so far...

Now, with even more mass we know that the forces that hold the nucleus together collapse... So I'm wondering what evidence we have that would indicate that a black hole is not just 1 giant quark-filled neutron... In other words, couldn't the black hole just be another level of collapse down to the quark level instead of the neutron level? The resulting mass would be very small, but not infinitely small, and how can we observe it to verify that this is not the case?

Edit: I'm suspecting that it may have something to do with the force necessary to actually bend spacetime back on itself and the consequence of doing so. (i.e. the elimination of distance and size)

 

[mathman]

The idea that a black hole is a singularity is derived from the equations of General Relativity. However, at these extreme conditions GR and quantum theory conflict, so nobody really knows what it is like inside a black hole. Your guess is as good as any.

 

[Felgar]

Cool... Yeah it just always seemed intuitive to me that another level of collapse would be logical... Thanks for the response.

 

[Coughlan]

I would have to think that black holes are hot. Imean if they exert enough gravity to not allow even photons to escape then, there must be a massive amount energy present, therefor hot.

 

[LURCH]

Personally, I tend to think that the final collapse to the state of "security" never actually occurs due to time dilation. You've heard that an object of falling into a black hole never quite reaches the center, right? As the object continues to progress closer and closer to the center, Time slows down, and the final moment of that object's journey takes forever. I think that this condition must also apply to the original mass that collapsed to form the black hole. So the original mass is still there in the center, shrinking toward zero, but contracting more and more slowly and sewing never quite reaching singularly.

 

[Felgar]

Very interesting way to look at it Lurch... Makes a lot of sense to me...

Although, time would also be getting dragged in with the mass... I'm having a hard time visualizing that. :)

 

[fat.farmer]

I don't think black holes are hot, because gravity must be so strong that particles cannot move??!??

 

[Entropy]

Current estiments on black hole temperature is somewhere around 2.7K. Although they are very cold compared to what we are use too, they have, like hot objects, very high entropy. In fact the entropy, mass and size of a black hole are all proportional. The maximum amount of entropy you can have (according to some of the books I've read) in space N is in a black hole of size N. You can't add more entropy to the black hole without adding to it's size and therefore mass.

Some theories say that around the singularity there is some type of quantum foam and that the center is just one string. But they're all pretty speculative.

 

[s3nn0c]

There are two interesting articles which can help you imagine that... we know so little about black holes :-)

http://arxiv.org/abs/hep-th/0401115

Quote:

"We argue that bound states of branes have a size that is of the same order as
the horizon radius of the corresponding black hole. Thus the interior of a black
hole is not ‘empty space with a central singularity’, and Hawking radiation can
pick up information from the degrees of freedom of the hole."

Check this article for interesting suggestions about internal structure of black holes in string theory. And here...

http://arxiv.org/abs/gr-qc/0411009

...is interesting phenomenon. Quote:

"It was argued recently that there exists an unexpected phenomenon, the reflection of incoming particles on the event horizon of black holes (Kuchiev(2003)). This means that a particle approaching the black hole can bounce back into the outside world due to those events that take part strictly on the horizon."

 

[Chronos]

There is some sentiment in favor of another level of collapse between a neutron star and a black hole. It is called a strange, or quark star. There is also some suspicion that certain neutron stars may have quark cores. There is even speculation that even denser states may be possible - preon stars! As do a number of reputable theorists, I resist the notion that black holes are infinitely dense, dimensionless points. Singularities are mathematical artifacts. Quantum theory suggests nature abhors a singularity with at least as much fervor as it does a vacuum. Some interesting recent papers on compact stars for those interested:

Hybrid stars that masquerade as neutron stars
http://arxiv.org/abs/nucl-th/0411016

Distinguishing Bare Quark Stars from Neutron Stars
http://arxiv.org/abs/astro-ph/0407091

Preon stars: a new class of cosmic compact objects
http://arxiv.org/abs/astro-ph/0410417

 

[Felgar]

My thoughts exactly Chronos. :)

 

[Zeteg]

Although they are very cold compared to what we are use too, they have, like hot objects, very high entropy. In fact the entropy, mass and size of a black hole are all proportional. The maximum amount of entropy you can have (according to some of the books I've read) in space N is in a black hole of size N. You can't add more entropy to the black hole without adding to it's size and therefore mass.

I've heard that it's uncertain if black holes actually have entropy. Since the only radiation we can sense from a black hole is the slight virtual photon that's thrown from its event horizon. Am I wrong? Do you have an article or something that I can read? :D