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The simplest definition of a black hole is an object that is so dense that not even light can escape its surface. But how does that happen?

The concept of a black hole can be understood by thinking about how fast something needs to move to escape the gravity of another object – this is called the escape velocity. Formally, escape velocity is the speed an object must attain to "break free" of the gravitational attraction of another body.

A black hole has two basic parts. The singularity is at the center and is where the mass resides. The event horizon is the boundary that marks where the escape velocity from the mass is the speed of light.


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If light can't escape a black hole, how can we see black holes?

Astronomers don't exactly see black holes directly. Instead, astronomers observe the presence of a black hole by its effect on its surroundings. A black hole, by itself out in the middle of our galaxy would be very difficult to detect.

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Supermassive black holes are found at the center of nearly every large galaxy. Exactly how supermassive black holes form is an active area of research for astronomers. Recent studies have shown that the size of the black hole is correlated with the size of the galaxy, so that the there must be some connection between the formation of the black hole and the galaxy.

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