Boötes I

The Boötes Dwarf Galaxy (Boo I dSph) is a galaxy discovered in 2006, which appears faint, with a luminosity of 100,000 L_☉ and an absolute magnitude of –5.8. It lies about 197,000 light-years (60.4 kiloparsecs) away in the constellation Boötes. This dwarf spheroidal galaxy appears to be tidally disrupted^[1] by the Milky Way Galaxy, which it orbits, and has two stellar tails that cross over to form a cross.^{[citation needed]} Tidally disrupted galaxies usually only form one tail.^{[citation needed]} The galaxy appears to be significantly elongated, with an ellipticity of ε = 0.68 ± 0.15.^[3]

Boötes Dwarf Galaxy
SDSS image of Boo I
Observation data (J2000 epoch)
Constellation	Boötes
Right ascension	14h 00m 06s[1]
Declination	+14° 30′ 00″ ± 15″[1]
Distance	197 ± 18 kly (60 ± 6 kpc)[1]
Apparent magnitude (V)	13.1[a]
Characteristics
Type	dSph[1]
Apparent size (V)	26.0′ ± 1.4′[1]
Other designations
Boo dSph, Boötes Satellite, Boötes Dwarf Spheroidal Galaxy, Boötes dSph galaxy,[2] PGC 4713553

Like many of the ultrafaint dwarf spheroidals, the entire galaxy appears fainter than the Rigel system (absolute magnitude –7.84).^[4] Even so, it is one of the more luminous UFDs.^[5] It is metal-poor, like other UFDs, with a mean metallicity of −2.34.^[5]

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.^[6]

Notes

1. ^{^} Apparent magnitude = Absolute magnitude + Distance modulus = –5.8^[1] + 18.9^[1] = 13.1