system
Given the following post, respond as if you're commenting on Reddit:
human
How do we differenciate between dark matter and black holes?

you cant see them, you can only calculate their position by studying their gravital influence on other objects. 

how do you know if you got a black hole or dark matter?
gpt
Dark matter is a general term for the missing non-luminous matter that makes up about 80% of the mass of the universe. There have been multiple candidates for this, and not all of them were exotic particles. This did include black holes, but also mundane objects like brown dwarfs (massive Jupiters, not quite big enough to be a star). These were ruled out as the main component of dark matter, because if dark matter is made up of small dense objects like black holes or brown dwarfs, they would from time to time line up with a star, and their gravity would bend the light of the star and give us a "lensing" signal. But all of the "lensing" we see can be explained by the visible stars, so there doesn't seem to be some large hidden population of individual massive objects. Instead, dark matter is generally considered to be some sort of subatomic particle that doesn't interact via electromagnetism. Neutrinos already act like that, but they are too light and move too quickly. So we're looking for something that's basically like a neutrino but more massive.

When we talk about "dark matter" these days, we usually do mean a smooth distribution of subatomic particles spread across the galaxy. This behaves very differently to an extremely dense massive object like a black hole. Dark matter forms massive but very spread-out galaxy-sized halos with gentle gravity slopes. A black hole only significantly affects stuff that's very close to it, but it has an extreme effect on stuff nearby, ripping stars apart to form accretion discs that become very hot and bright and rotate incredibly fast. Dark matter is almost like a "fluid" (technically a "collisionless fluid" following the Boltzmann equation), because it's made up of a smooth distribution of subatomic particles, while black holes are individual massive objects, as massive as a star or more.