Ursa Major I Dwarf

Ursa Major I Dwarf
Observation data (J2000 epoch)
Constellation Ursa Major
Right ascension 10h 34m 52.8s[1]
Declination +51° 55′ 12″[1]
Distance 330,000 light-years (100 kpc)[2]
Type dSph
Other designations
UMa I dwarf,[1] Ursa Major I dSph[1]

Ursa Major I Dwarf (UMa I dSph) is a dwarf spheroidal galaxy orbiting the Milky Way galaxy. The discovery by Beth Willman et al. was announced in 2005.[2]

Being a small dwarf galaxy, it measures only a few thousand light-years in diameter. As of 2006, it is the third least luminous galaxy known (discounting possible dark galaxies such as VIRGOHI21 in the Virgo cluster of galaxies), after the Boötes Dwarf (absolute magnitude −5.7) and the more recently discovered Ursa Major II Dwarf (absolute magnitude −3.8). The absolute magnitude of the galaxy is estimated to be only −6.75,[2] meaning that it is less luminous than some stars, like Deneb in the Milky Way. It is comparable in luminosity to Rigel. It has been described as similar to the Sextans Dwarf Galaxy.[2] Both galaxies are ancient and metal-deficient.

It estimated to be located at a distance of about 330,000 light-years (100 kpc) from the Earth.[2] That is about twice the distance to the Large Magellanic Cloud; the largest and most luminous satellite galaxy of the Milky Way.

There was another object called Ursa Major Dwarf, discovered by Edwin Hubble in 1949.[3] It was designated as Palomar 4. Due to its peculiar look, it was temporarily suspected to be either a dwarf spheroidal or elliptical galaxy. However, it has since been found to be a very distant (about 360,000 ly) globular cluster belonging to our galaxy.

See also

References

  1. 1 2 3 4 "NASA/IPAC Extragalactic Database". Results for Ursa Major dSph. Retrieved 2006-11-27.
  2. 1 2 3 4 5 Willman, Dalcanton, Martinez-Delgado, et al. (2005) "A New Milky Way Dwarf Galaxy in Ursa Major", submitted to Astrophysical Journal Letters, on arXiv.org: astro-ph/0503552
  3. ↑ "Ursa Major Dwarf, Palomar 4". Milky Way Globular Clusters. Retrieved April 16, 2005.

External links

Coordinates: 10h 34m 52.8s, +51° 55′ 12″

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