The Boötes Dwarf Galaxy (Boo I dSph) is a galaxy discovered in 2006, which appears faint, with a luminosity of and an absolute magnitude of –5.8. It lies about away in the constellation Boötes. This dwarf spheroidal galaxy appears to be tidally disrupted by the Milky Way Galaxy, which it orbits, and has two stellar tails that cross over to form a cross. Tidally disrupted galaxies usually only form one tail. The galaxy appears to be significantly elongated, with an ellipticity of .
Like many of the ultrafaint dwarf spheroidals, the entire galaxy appears fainter than the Rigel system (absolute magnitude –7.84). Even so, it is one of the more luminous UFDs. It is metal-poor, like other UFDs, with a mean metallicity of −2.34.
The stellar population of Boötes I is mostly very old stars. The two populations have essentially the same age, 13.4 billion and 13.3 billion years, respectively, with most of the stars being of the latter population.
Notes
Apparent magnitude = Absolute magnitude + Distance modulus = –5.8 + 18.9 = 13.1
References
External links The Universe within 500,000 light-years The Satellite Galaxies (Atlas of the Universe) Two New Galaxies Orbiting the Milky Way (Ken Croswell) April 19, 2006 Strange satellite galaxies revealed around Milky Way Kimm Groshong (New Scientist) 17:00 24 April 2006 New Milky Way companions found: SDSS-II first to view two dim dwarf galaxies (SDSS) May 8, 2006 Astronomers Find Two New Milky Way Companions (SpaceDaily) May 10, 2006 Boötes Dwarf Galaxy at Constellation Guide