September 17, 2008--The ultra-faint Segue 1 is dominated by dark matter like no other known galaxy.

Segue 1 is almost a thousand times more massive than suggested by the light of its 24 known stars (right image). Dark matter accounts for most of its mass.

The left image reveals Segue 1's cosmic neighborhood, including foreground and background stars as well as the faint galaxy.

Segue 1 orbits the Milky Way but is a billion times less bright.