The Boötes Dwarf Galaxy (''Boo I dSph'') is a

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

discovered in 2006, which appears faint, with a

luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...

of and an absolute magnitude of –5.8. It lies about away in the constellation

Boötes Boötes ( ) is a constellation in the northern sky, located between 0° and +60° declination, and 13 and 16 hours of right ascension on the celestial sphere. The name comes from , which comes from 'herder, herdsman' or 'plowman' (literally, 'o ...

. This

dwarf spheroidal galaxy A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and as systems that are c ...

appears to be tidally disrupted by the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

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 Rigel is a blue supergiant star in the constellation of Orion. It has the Bayer designation β Orionis, which is Latinized to Beta Orionis and abbreviated Beta Ori or β Ori. Rigel is the brightest and most massive componentand ...

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 In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

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 Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
= Absolute magnitude +
Distance modulus The distance modulus is a way of expressing distances that is often used in astronomy. It describes distances on a logarithmic scale based on the astronomical magnitude system. Definition The distance modulus \mu=m-M is the difference between th ...
= –5.8 + 18.9 = 13.1

References

External links

The Universe within 500,000 light-years The Satellite Galaxies
(Atlas of the Universe)

(Ken Croswell) April 19, 2006

Kimm Groshong (New Scientist) 17:00 24 April 2006

(SDSS) May 8, 2006

(SpaceDaily) May 10, 2006
Boötes Dwarf Galaxy at Constellation Guide
{{DEFAULTSORT:Bootes 1 Dwarf spheroidal galaxies Local Group Milky Way Subgroup Boötes 4713553