## Everybody loves black holes (part II)

In a way, black holes are pretty simple. They have only three properties: mass, charge and spin. If two black holes have equal values of only these three things, they are indistinguishable.

You might already know that when certain stars die, the result is an object that is dense beyond imagination, so that it collapses under its own gravity into an infinitely small point, which we call a singularity. Gravity around the singularity is strong enough to prevent light from escaping, the boundary of where the gravity is this strong is referred to as the “event horizon”, which is a very catchy name, but does what is says it does. There is no information of any kind that survives crossing this line.

Black hole in 3...2... (well, it actually takes a while, but you get the idea)

They don’t have to be any particular mass, theoretically that can be as small as you can imagine (or smaller), but they do have to be VERY dense. The only natural processes we know of that make them, make them pretty massive. Some are a few solar masses (our sun = 1 solar mass), some are millions or even billions of solar masses. The big ones you’ll find at the center of galaxies, some spewing out GARGANTUAN jets. Note that these jets don’t come out of the black hole itself, nothing does, but are a side effect of matter being drawn into oblivion.

That bright point is M87, a galaxy more than twice the size of the Milky Way, so those jets are BIG.

From there things can quickly get more complicated. The way black holes mess with space-time is pretty wild. Gravity can be represented as a distortion of space-time, often visualized in analogies involving bowling balls sitting on trampolines. The heavier (or denser) the object on the trampoline, the deeper the indentation. Think of a black hole as an infinitely deep indentation, which would incidentally always look black if you peered down into it, even if you shined a light into its depths. It’s a pretty good analogy!

This example puts things in a two dimensional format though, since we can’t imagine what an indentation in three dimensional space would look like. If you add light to your trampoline analogy though, it would be traveling across the surface of it, so when you distort its path, it’s observable. You don’t need a black hole to do this, we now observe this around massive things like galaxy clusters, but a black hole out in the open would do this intensely.

Gravitational lensing in action.

In the next 30-50 years, we may finally be able to directly observe a black hole. I have a feeling doing this will deliver both expected results and a ton of new questions. If you go here, you’ll get a fancier and more interactive introduction to black holes.

I’m going to save the explanation of what you might experience if you were to get sucked into a black hole for part III.