What does the no-hair theorem say about the exterior description of black holes?

• A. External properties depend on mass and radius only.
• B. Mass, electric charge, and angular momentum fully describe the black hole.
• C. Temperature and color determine exterior appearance.
• D. Only the event horizon exists; interior properties do not affect external fields.

Answer: (B)

The no-hair idea is that the exterior spacetime of a black hole is completely specified by just three quantities: mass, electric charge, and angular momentum. No matter what formed the black hole or what fell into it, those details don’t leave fingerprints on the outside; the spacetime settles into a Kerr–Newman geometry described entirely by M, Q, and J.

That’s why the answer listing mass, charge, and angular momentum as the full description is the best choice. In astrophysical cases the charge is often tiny, so the exterior is effectively described by mass and angular momentum through the Kerr solution, but the three quantities together capture the full external description.

The other options don’t fit because they either mix in quantities that aren’t independent descriptors of the external field (like a single radius) or invoke properties (temperature, color) that don’t govern the outside geometry. And saying only the event horizon exists and interior properties don’t affect external fields misses the precise point: the outside is determined by the three global parameters, not by whatever interior details happened to fall inside.