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What is a black hole?

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Quick answer

A black hole is a region of space where gravity is so strong that nothing — not even light — can escape once it crosses the boundary called the event horizon. They form when massive stars collapse at the end of their lives.

Key things to understand

  1. The event horizon is the point of no return; anything crossing it cannot get back out.
  2. At the center is the singularity, where matter is crushed to near-infinite density.
  3. Black holes are not cosmic vacuum cleaners — you only fall in if you cross the event horizon; otherwise you can orbit one like any massive object.
  4. Supermassive black holes, millions to billions of times the Sun's mass, sit at the center of most galaxies, including our Milky Way.

People also ask

Can we see a black hole?
Not directly, since light can't escape. We see them by their effects: glowing superheated matter swirling around them, and the bending of light. The first image of one was captured in 2019.
What happens if you fall into a black hole?
Tidal forces stretch you out in a process nicknamed 'spaghettification.' From far away, you'd appear to freeze and fade at the event horizon due to extreme time dilation.
How big can a black hole get?
Supermassive black holes can exceed billions of times the Sun's mass. The one in our galaxy, Sagittarius A*, is about 4 million solar masses.

Part of the guide: Space & Astronomy →