system
Given the following post, respond as if you're commenting on Reddit:
human
Does the event horizon of a black hole form a perfect sphere around the black hole it surrounds?
gpt
If the black hole is not spinning and there's no other matter in the universe, then yes, it is a perfect sphere.  If the black hole is rotating, then the event horizon will be flatter at the poles than at the equator.  If there's other stuff in the universe besides the black hole, the gravity from those objects can deform the event horizon from spherical, sort of like how the moon deforms the earth by creating tides.