Violent people can give others a black eye -- and so can galaxies. South of the Big Dipper's handle, for example, in the constellation Coma Berenices, there's a large spiral galaxy that got a black eye when another galaxy smashed into it a billion years ago.
Astronomers first spied the Black-Eye galaxy centuries ago, before anyone knew its nature.
English astronomer Edward Pigott discovered it in March of 1779. A couple of weeks later, German astronomer Johann Bode independently found the object, and a year later, so did French comet hunter Charles Messier. At the time, Messier was compiling a list of fuzzy celestial objects that looked like comets and could fool comet hunters like himself. The fuzzy object in Coma Berenices became number 64 on Messier's list, so today it's called M64 -- the M standing for Messier.
But M64 also has a more colorful name: the Black-Eye galaxy. Telescopes show that one side of the galaxy has an enormous lane of dust, which absorbs the light of the stars behind it. A billion years ago, a small, dusty galaxy hit M64, dumping its dust into the larger galaxy. Gas in M64's outer regions revolves in the opposite direction from most of the galaxy's stars, providing further evidence that something hit the galaxy and gave it a black eye.
Unlike people, though, M64 actually benefits from its black eye. The collision has triggered the birth of new stars that make the galaxy shine more brightly.
Script by Ken Croswell, Copyright 2009
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