No-Hair Theorem
A black hole is completely characterized by only three properties: mass, electric charge, and angular momentum (spin), regardless of its initial complexity.
📜
The statement of the theorem
Consider the vacuum solution to the Einstein Field Equations () in the asymptotically flat limit. The theorem asserts that the metric tensor is uniquely determined by the three conserved charges: the mass , the electric charge , and the angular momentum . The resulting metric is the Kerr-Newman solution, which is characterized by the parameters alone.
Source: Wikipedia