September 20, 2002 | David F. Coppedge

How Did Blue Stars Get So Close to a Black Hole?

Every solution breeds new problems, Murphy’s Law suggests.  Astronomers working with the Hubble Space Telescope feel that pain.  While finding confirming evidence for a supermassive black hole at the center of the Andromeda Galaxy M31, they are perplexed to see a disk of hot blue stars orbiting it too close for comfort.  Estimated to be 200 million years old, the 400+ stars are in a tight orbit a light-year across and careening around the black hole at 2.2 million mph.
    Blue stars are thought to be short-lived and could not have formed so close to the black hole; the extreme tidal forces there should tear the matter apart and prevent collapse into stars.  “Gas that might form stars must spin around the black hole so quickly that star formation looks almost impossible,” said one astronomer, “But the stars are there.”  They said this is like watching a magician pull a rabbit out of a hat.  “You know it happened but you don’t know how it happened.”  Since even younger stars have been found orbiting the presumed black hole at the center of the Milky Way, maybe this “odd activity” is the norm.

Puzzles are good for scientists, and better observations are welcomed like rain in a desert, but scientists also need to learn to think outside the box.  One question never asked is whether these stars really are 200 million years old.

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