Photo: Tiny Galaxies Shed New Light on Dark Matter

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From left to right, the dwarf galaxies known as W1, Leo II, and Fornax display varying degrees of brightness.

Astronomers have known that these and other dwarf galaxies orbiting the Milky Way range in brightness from a thousand times to ten million times the luminosity of the sun.

But a study released in August 2008 says that 18 of the 23 known satellite galaxies have a common central mass, a finding that sheds light on how the enigmatic substance known as dark matter helps galaxies form.

Image courtesy J. Bullock, M. Geha, and R. Powell

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