system
Given the following post, respond as if you're commenting on Reddit:
human
Would a black hole have surface irregularities of mere atoms? How does it's gravity affect how smooth it's surface is?
gpt
In general relativity, black holes have no surface at all.  The *event horizon* that people talk about is not a physical barrier, it's a mathematical point of no return. In the current understanding of gravity (though alternate theories exist) the mass of the black hole is concentrated into a single point with no volume, and consequently no surface, called the singularity. Regardless of the theory, certainly there is no longer any atomic structure at all. The most compact objects (with surfaces) that we know about are neutron stars, which have envelopes and crusts of atomic species where the pressure is less, but which break down into a material that is even denser than the nucleus of an atom. Atoms certainly are not the structure of material deep inside of neutron stars. 

Since neutron stars are the densest objects we know of with surfaces, we can answer your question in regards to them instead of black holes. The outer crust of a neutron star can have small "mountains" on it, and a quick back-of-the-envelope calculation shows that they can't be reasonably be larger than ~1 cm because the gravity is so strong that it will pull down anything higher than that (similar to how there's a maximum height for mountains on Earth or Mars or any other planet based on the strength of gravity at the surface). As the neutron star spins, these "mountains" create an asymmetric moment of inertia and should emit gravitational waves. Instruments like LIGO are currently trying to detect these gravitational waves (in addition to much louder-but-shorter ones like merging neutron stars).