What is the Virgo Stellar Stream?

The Virgo Stellar Stream covers over 100 square degrees, and possibly as much as 1,000 square degrees. Despite its proximity to the solar system and the solid angle that it consequently covers, the stream contains only a few hundred thousand stars. The low surface brightness of the galaxy may have militated against its detection in surveys before SDSS. The stream lies within the Milky Way, approximately 10 kiloparsecs from the Sun, and extending over a region of space at least 10 kpc across in three dimensions. It is close to the plane of the sky to the Sagittarius Dwarf Elliptical Galaxy, which was found in 1994 through a similar photometric analysis of a star survey. The number of stars in the stream is not greatly in excess of a star cluster, and it has been described by a member of the team that discovered it as a rather pathetic galaxy, in comparison to the Milky Way. Many of the stars have been known for centuries and thought of as normal Milky Way stars, although they have a lower metallicity than normal Population I stars in the Milky Way.

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