system
Given the following post, respond as if you're commenting on Reddit:
human
Is the event horizon of a black hole actually a perfect sphere?

It just occurred to me that if the minute amounts of "gravity" from all the other mass in the universe would distort the shape of the event horizon, even if itis ever so slightly.
gpt
The most common presentation of a blackhole is as a vacuum solution: you have some amount of mass (which may be carrying charge and/or angular momentum) located at a single point and then *nothing else anywhere*. In the non-rotating case this predicts a spherical event horizon, but even in that case if you add in other effects (such as the contribution from matter in other regions of space), the shape of spacetime around the event horizon will be perturbed in such a way that it will not, in general, be *perfectly* spherically symmetric. However, except in rare cases such as black-hole collisions, the deviations from a perfect sphere will tend to be quite small.