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The Question

(Submitted January 23, 1998)

I want to know how a black hole that is so small that it is only 2 to 3 kilometers big can pull an entire star into its crevice.

The Answer

How does a mouse eat an elephant? One bite at a time.

A black hole in a close orbit around a star can pull the top layers of the star off the surface and down its own gravity well. Once the material passes beyond the black hole's event horizon, it is gone, and more stuff can be consumed by the black hole. You are left with a slightly larger black hole, and a slightly less massive star, so the black hole can pull a little more material off the star. This continues until the star is gone, and the black hole's hunger is yet unabated.

David Palmer
for Ask an Astrophysicist

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