Boötes III is an overdensity in 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 ...

halo HALO, halo, halos or haloes may refer to: Most common meanings * Halo (optical phenomenon) * Halo (religious iconography), a ring of light around the image of a head * ''Halo'' (franchise), a sci-fi video game series (2001–2021) Arts and en ...

, which may be a disrupted

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 ...

. It is situated 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 ...

and was discovered in 2009 in the data obtained by

Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...

. The galaxy is located at the distance of about 46 kpc from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

and moves away from it at the speed of about 200 km/s. It has an elongated shape ( axis ratio of 2:1) with the radius of about 0.5 kpc. The large size and an irregular shape may indicate that Boötes III in a transitional phase between a gravitationally bound galaxy and completely unbound system. Boötes III is one of the smallest and faintest satellites of the Milky Way—its integrated luminosity is about 18,000 times that of the Sun (absolute

visible magnitude Apparent magnitude () is a measure of the 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 of the object's light cau ...

of about −5.8), which is much lower than the luminosity of many

globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

s. The mass of Boötes III is difficult to estimate because the galaxy is in process of being disrupted. In this case the

velocity dispersion In astronomy, the velocity dispersion (''σ'') is the statistical dispersion of velocities about the mean velocity for a group of astronomical objects, such as an open cluster, globular cluster, galaxy, galaxy cluster, or supercluster. By measu ...

of its stars is not related to its mass. The stellar population of Boötes III consists mainly of moderately old stars formed more than 12 billion years ago. The

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 these old stars is low at , which means that they contain 120 times less heavy elements than the Sun. Boötes III might be the source of stars of the Styx stream in the

galactic halo A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. Several distinct components of a galaxy comprise its halo: * the stellar halo * the galactic corona (hot gas, i.e. a plas ...

, which was discovered together with this galaxy.

References

{{DEFAULTSORT:Bootes Iii (Dwarf Galaxy) Dwarf spheroidal galaxies 4713562 Boötes Local Group Milky Way Subgroup ?