They can be completely characterized by only mass, charge, and spin, according to the no-hair theorem.
The Reissner-Nordstrom solution to Einstein's equations describes one of these with charge, and the Kerr solution describes a rotating one. The constant of proportionality for their entropy is k over 4 Planck lengths, and is proportional to surface area. String theorists describe them as "fuzzballs", and they indirectly cause the Lense-Thirring effect. "Mini" ones may have formed by the Big Bang, although they evaporate through Hawking Radiation. They can be completely characterized by only mass, charge, and spin, according to the no-hair theorem. Resulting from the collapse of a massive star, for 10 points, what astronomic object is surrounded by event horizon and possesses a singularity, where gravity becomes infinite?
The Reissner-Nordstrom solution to Einstein's equations describes one of these with charge, and the Kerr solution describes a rotating one.
{Black hole}