• Moiya McTier

Astronomy Fun Fact #64

Earlier this year (April 2019), astronomers released the first ever picture of the event horizon of a black hole. It was super exciting! But it also caused some confusion because people kept saying it was a picture of the black hole itself, which it wasn't.

Black holes are so dense that light can't escape. Another way of saying this is that the escape velocity in a black hole (the speed something has to have in order to escape an object's gravitational pull) is greater than the speed of light. As you move farther away from an object, its gravity gets weaker and the escape velocity decreases.

The event horizon is the distance from the center of the black hole where the escape velocity drops below the speed of light, so light can get out.

So that's what astronomers took a picture of -- the light around the black hole, not the black hole itself.

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