Wikipedia:Reference desk/Archives/Science/2019 June 19

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June 19

Black holes

What is the internal temperature of a typical black hole? And why? 86.8.201.134 (talk) 01:00, 19 June 2019 (UTC)

If I'm reading Black hole correctly, it's very close to absolute zero, and it has to do with a lack of internal energy. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:06, 19 June 2019 (UTC)

You are not reading correctly. The low temperature mentioned (a few nanokelvin) is the temperature of its horizon, not its surface, and not the internal. The typical black hole sucks energy (=mass) out of the 2.7K background radiation more than it loses, and has tons (so to speak) of internal energy. Gem fr (talk) 09:47, 19 June 2019 (UTC)

My understanding is that black hole thermodynamics struggles to answer this very question, still open. Said otherwise: we cannot answer Gem fr (talk) 09:47, 19 June 2019 (UTC)

The issue is "where" in the black hole you look. As a corollary, consider the bottom of the ocean. Due to pressure, the water at the bottom of the ocean is forced to be as condensed as possible. When water is as dense as possible, it will be about 3C or 35F. The pressure is the primary factor in the resulting temperature. But, if you go up, pressure decreases and the temperature can be influenced by other factors. In stellar pressure systems like neutron stars and black holes, it gets very weird. Models of neutron stars are attempting to work out what happens when the pressure on matter is so high that electrons and protons merge to form neutrons. Then, everything is a neutron, commonly called neutron matter. What is the temperature of neutron matter? It is very close to absolute zero because any energy that exists is barely enough to keep the neutron from collapsing. In other words, the density of the neutrons inhibits energy which inhibits temperature. Inside a black hole, neutrons should collapse into quark matter. The energy keeping the neutrons stable is lost. With less energy, there is lower temperature. An expected model is that inside the event horizon, there is inward rushing matter that collapses around the singularity first as neutron matter. Inside that it collapses into quark matter. Inside that, it collapses further into a singularity, but bosons create a huge problem. They don't collapse (theoretically). So, is the singularity a mess of boson matter? If so, can it retain energy? What if bosons have nothing to do with it? What if it all collapses into string energy? Without mass, in the relative sense, what is the temperature of a singularity of pure energy? That makes no sense. Hopefully, it does make sense that there is a big hunch that once inside the event horizon temperature will drop quickly towards absolute zero. But, when you hit the singularity, temperature no longer has meaning. 12.207.168.3 (talk) 17:49, 19 June 2019 (UTC)

I'm not really following that logic, and our neutron star article says they have temperatures ranging from 10¹² to 10⁶ Kelvin, which is surely not 'near' absolute zero in anything less than the most cosmic sense. Wnt (talk) 04:15, 28 June 2019 (UTC)