What do black holes look like? And What’s inside a black hole?

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What do black holes look like?  And 

What’s inside a black hole?

Black holes themselves are invisible—they emit virtually no light and so cannot be seen directly. But we have developed several ways to find them anyway.

By looking for the stuff that’s falling in. If material is falling into a black hole, it travels at such high speeds that it gets hot and glows very brightly, and we can detect that. (That’s how the Event Horizon Telescope took its famous first images of black holes.) Scientists hope to use this method to learn a lot more about how and what black holes “eat.”

By seeing their gravity pulling on other things. We can find black holes by watching the movements of visible objects around them. For example, a black hole’s gravity is so strong that nearby stars will orbit around them, so we can look for stars behaving strangely around a patch of “empty” space. From this, we can calculate exactly how heavy that black hole must be. That’s how Nobel Prize winner Andrea Ghez and her team detected the supermassive black hole at the center of our own galaxy.

“In some ways that’s one of the most profound questions in physics,” said University of Chicago Prof. Daniel Holz. “There are not many cases in physics where we simply cannot predict what happens, but this is one of them.”

Black holes have two parts. There is the event horizon, which you can think of as the surface, though it’s simply the point where the gravity gets too strong for anything to escape. And then, at the center, is the singularity. That’s the word we use to describe a point that is infinitely small and infinitely dense.

“Very near the singularity, one would expect quantum effects to become important. However, we don't yet have a quantum theory of gravity (or, at least, one capable of reliably making such predictions), so we just don't know the correct description of the singularity—or even whether it really is a singularity,” said University of Chicago Prof. Robert Wald.

Scientists think that black holes eventually will explode, but it will take many, many times longer than the current age of the universe for that to happen. What will it look like when that happens? That’s another big mystery.

“Maybe there’s a little nugget left behind containing all of the information that fell into the black hole, maybe there’s a portal to a new universe, maybe the information is just gone forever; we simply don’t know,” said Holz.