A black hole is a place in space where gravity is so strong that even light cannot get out. Black holes are invisible, because no light comes out of them. Black holes do not roam around space eating stars and planets. Far away, a black hole pulls only as hard as any object of the same mass, so planets and stars can orbit it safely. Only things that get too close fall in. Gravity can be too strong to escape from. To leave Earth you need to go about 11 kilometers per second, but inside a black hole's event horizon you would need to go faster than light.

Almost every large galaxy has a supermassive black hole at its center. The black hole in the middle of the Milky Way, called Sagittarius A*, has about 4 million times the mass of the Sun. Stars near the center of our galaxy orbit an unseen mass; the star S2 came closest to Sagittarius A* in May 2018, which helped show the black hole is there. Sagittarius A* is quiet and starved of matter, yet the Webb telescope sees flares and flickers from it. In 2022 scientists showed the first picture of the black hole at the center of our galaxy. Space telescopes can help find black holes, even though we cannot see the black holes themselves.

Black holes come in different sizes. The biggest black holes are called supermassive black holes. Some black holes have as much mass as millions of Suns. Supermassive black holes can merge when their galaxies collide, and they can grow by eating gas and stars. As of November 2026, black holes of medium size should exist between small stellar black holes and giant supermassive ones, but they are hard to confirm. Some supermassive black holes already existed in the universe's first billion years, and how they grew so big so fast is still unsolved.

Einstein's general theory of relativity (1915) is where black holes come from. In 1916 the same theory predicted gravitational waves. On September 14, 2015, detectors in Louisiana and Washington caught ripples in space from two black holes crashing together. The 2015 LIGO detection was the first time scientists ever caught two black holes merging, a collision that had been predicted but never observed. The two black holes in the first LIGO detection (about 29 and 36 Suns) merged into one of about 62 Suns. About 3 Suns of mass left as gravitational waves. The first black hole merger ever detected happened about 1.3 billion years ago, roughly a billion light-years away.

Most stellar-mass black holes we have found are paired with a normal star, and the hot gas pulled from the star glows in X-rays and gives the black hole away. The glowing disk of gas around a black hole, called the accretion disk, is the main source of light we can see. In 2019 scientists showed the first picture of a black hole, in a galaxy called Messier 87. The bright ring in the picture of M87's black hole is light from hot gas that is bent around the black hole, and the dark middle is its shadow. As of November 2026, the shadow of the black hole in galaxy M87 is about 38 billion kilometers across, and the black hole has a mass of roughly 6.5 billion Suns.

Words to know

• orbit: move around
• flares: bright bursts
• accretion: falling together
• merged: joined together
• unsolved: not answered