The dwarf galaxy lies in the direction of the constellation Virgo and is, on average, about 30,000 light-years away from Earth. It also covers an area of the night sky roughly 5,000 times larger than the full moon. Yet it contains perhaps only a million stars, making it "a rather pathetic galaxy," compared to the Milky Way, said research team member Robert Lupton of Princeton University. "It is very, very diffuse."

Lupton and colleagues discussed their discovery at the American Astronomical Association's annual meeting. He said the Sloan instrument, a wide-angle, 2.5 meter mirror located in Sunspot, New Mexico ¿ which he called "the ugliest telescope in current use" ¿ so far has imaged more than one-fifth of the northern sky. By measuring the colors and brightness of nearly 50 million stars, the astronomers inferred their distance and created what amounts to a 3-D map of the galaxy.

Within that map, they discovered an anomaly: A fuzzy cloud of stars that does not fit within the galaxy's three main components: its flattened disk of stars, its central bulge, or its spherical stellar halo. Instead, Lupton said, there seems to be a cloud of stars stuck above the galactic plane. "Almost certainly it is a dwarf galaxy being cannibalized," he said.

Eventually, Lupton added, the galaxy's much bigger gravity will pull the dwarf companion fully inside. "It will be part of the Milky Way in about 1 billion years," he said.

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