#stem is cool

The name is such a misnomer! In fact black holes in our universe tend to be some of the brightest things there are!

Why? because the immense gravity of a black hole tends to pull matter towards it, in tight orbits, and once close enough, into a whirlpool of sorts that enters into the black hole. Matter including things like stars! so a black hole might not itself produce light but it is surrounded by a bunch of things there are. Saying a black hole is a "light ring with a black inside" would actually be more physically accurate.

In addition, that matter, as it accretes around the black hole, it gets super hot and actually glows. This forms quasars, which are (I'm pretty sure) the most energy-efficient way to turn matter into energy in the universe, and hopefully one day we can control this process artificially with mirrors to extract this energy for human use. Here is what quasars look like:

By ESO/M. Kornmesser - http://www.eso.org/public/images/eso1122a/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=15700804

So black holes aren't black. Yes, anything within the event horizon (Schwarzschild radius) is black but black holes in general look more like Gargantua in Interstellar than pure black regions of space.

Yes, there are no ideal spherical cows in a vaccum in the Universe. But approximations work to give us results. And that's why theories can allow us to make the calculations to describe the Universe quantitatively.

For instance, yes, the Sun is not a perfect uniform sphere. But with the approximation that it is, we can calculate the trajectories of the planets to meticulous detail. Yes, the interior of a star is technically not a steady-state spherically-symmetric fluid. But with the approximation it is, we can make useful predictions about stellar behavior. Yes, the hydrogen atom is not as simple as a one-electron system under a Coulomb potential. But with the approximation it is, we were able to make predictions extremely close to observed values. And finally, yes, perfect smooth functions do not exist in nature. But using the approximation they are, we can use the power of analytical techniques, calculus, geometry, functional analysis, and differential equations to perform highly-accurate calculations and predictions of incredibly many phenomena. Approximations have worked so well that in many cases we don't even know when they don't work until we uncovered new things that we can't explain using them.