system
Given the following post, respond as if you're commenting on Reddit:
human
What does it mean for a black hole to be rotating?

It seems unintuitive to me to describe a single point as rotating. In what direction does a singularity rotate?
gpt
Rotating black holes are believed to have a ring-shaped singularity, or Kerr singularity, because as you suspected a point cannot have angular momentum in classical physics.

However, quantum mechanics does allow for point particles to have angular momentum. This angular momentum called spin is an intrinsic property of fundamental particles like electrons and quarks as well as composite particles like protons and neutrons.