Extremal black hole
Template:Short description Template:More citations needed In theoretical physics, an extremal black hole is a black hole with the minimum possible mass that is compatible with its charge and angular momentum.<ref>Template:Cite journal</ref>
The concept of an extremal black hole is theoretical and none have thus far been observed in nature. However, many theories are based on their existence.
In supersymmetric theories, extremal black holes are often supersymmetric: they are invariant under several supercharges. This is a consequence of the BPS bound. Such black holes are stable and emit no Hawking radiation. Their black hole entropy<ref name=Bekenstein>Template:Cite journal</ref> can be calculated in string theory.
It has been suggested by Sean Carroll that the entropy of an extremal black hole is equal to zero. Carroll explains the lack of entropy by creating a separate dimension for the black hole to exist within.<ref name="Extremal limits and black hole entropy">Template:Cite journal</ref>
The Hawking radiation of extremal black holes is considered non-thermal (non-Planck distributed), with no associated temperature.<ref>Template:Cite journal</ref>
The hypothetical black hole electron is super-extremal (having more charge and angular momentum than a black hole of its mass "should").
The third law of black hole thermodynamics should disallow such an extremal black hole and in 1986 a proof was published<ref>Template:Cite journal</ref> by Werner Israel. Nevertheless, recent work in a pair of preprints claims it contains an error and therefore extremal black hole are indeed possible.<ref>Template:Cite arXiv</ref><ref>Template:Cite arXiv</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The third law of thermodynamics for black holes has always been controversial.
See alsoEdit
- Black hole information paradox
- Black hole thermodynamics
- Near-extremal black hole
- Quantum gravity
- Trans-Planckian problem
- Positive energy theorem