People used to think that the heavens were a vast clockwork, with planets and moons moving in circular orbits like a vast timepiece.  Recent advances have shown us that this stellar machinery is far vaster than they ever suspected – even our galaxy has satellites, mini-galaxies orbiting the Milky Way and some of them could be very interesting indeed.

We now know about two dozen of these satellite galaxies.  One of the most recent is "Segue 1", uncovered by the Sloan Digital Sky Survey (SDSS), whose extremely low light-to-mass ratio makes it a particularly significant cosmic find.  Despite having a mass of a million suns it is nowhere near as luminous as astronomers would expect, with only a couple of hundred stars visible. The ultra-faint galaxy is a billion times less bright than the Milky But despite its small number of visible stars, Segue 1 is nearly a thousand times more massive than it appears, meaning most of its mass must come from dark matter, according to the researchers.

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