In theoretical physics, an extremal black hole is a black hole with the maxium possible mass that can be compatible with a given charge and angular momentum. In other words, this is the smallest possible black hole that can exist while rotating at a given fixed constant speed.
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 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.
The hypothetical black hole electron is defined as an extremal black hole.
Famous quotes containing the words black and/or hole:
“(The black stream, catching on a sunken rock,
Flung backward on itself in one white wave,
And the white water rode the black forever.”
—Robert Frost (1874–1963)
“Someone had literally run to earth
In an old cellar hole in a byroad
The origin of all the family there.
Thence they were sprung, so numerous a tribe
That now not all the houses left in town
Made shift to shelter them without the help
Of here and there a tent in grove and orchard.”
—Robert Frost (1874–1963)