What is a black hole?

A black hole forms when a large amount of mass is packed into a tiny space — often when a massive star collapses at the end of its life. Gravity becomes so intense that beyond a boundary called the event horizon, the escape velocity exceeds the speed of light, so nothing can get out. At the core, matter is thought to collapse to a point of infinite density called a singularity. Black holes range from stellar-mass objects a few times heavier than the Sun to supermassive giants millions or billions of times the Sun’s mass at the centers of galaxies. In 2019 astronomers captured the first image of a black hole’s shadow in galaxy M87.