What is a Black Hole? We Asked a NASA Expert

What exactly is a black hole? Well, they’re not holes at all, rather incredibly dense regions in space with gravity so strong, not even light can escape.

There are stellar-mass black holes, which form when massive stars collapse and explode in a supernova, and supermassive black holes, which are millions to billions of times more massive and sit at the centers of galaxies.

Scientists know these cosmic powerhouses shape galaxies and influence how the universe evolves. But how do supermassive black holes form? That’s still one of astronomy’s biggest mysteries. A NASA scientist explains what we know (and don’t know) about these cosmic gargantuans.