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.<br /> <br />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.<br /> <br />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. <br />
