Sagittarius A* Holds About Four Million Times the Mass of the Sun

LIGO detected the ripples in spacetime on September 14, 2015, from two black holes that had collided over a billion years ago.

The X-ray source was discovered in 1964, and its behavior convinced many astronomers it was a black hole.

In 1974 Hawking showed that black holes should emit faint radiation and eventually evaporate, though the effect has never been observed directly.

The Event Horizon Telescope captured the glowing ring around the black hole at the center of galaxy M87, about 55 million light-years away.