Ursa Major I Dwarf (UMa I dSph) is a dwarf spheroidal galaxy that orbits the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

. It was discovered in 2005 within the

Ursa Major Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear," referring to and contrasting it with nearby Ursa ...

constellation and is the third least luminous known galaxy.

Discovery

It was discovered by

Beth Willman Beth Willman is an American astronomer who is the Executive Officer of the LSST (Large Synoptic Survey Telescope) Corporation, an astronomical organization notable for its support of the Vera C. Rubin Observatory. She was previously the deputy dir ...

, Julianne J. Dalcanton, David Martinez-Delgado, and Andrew A. West in 2005.

Properties

Being a small dwarf galaxy, it measures only a few thousand

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s in diameter. As of 2006, it is the third least luminous galaxy known (discounting possible

dark galaxies A dark galaxy is a hypothesized galaxy with no, or very few, stars. They received their name because they have no visible stars, but may be detectable if they contain significant amounts of gas. Astronomers have long theorized the existence of dark ...

such as

VIRGOHI21 VIRGOHI21 is an extended region of neutral hydrogen (HI) in the Virgo cluster discovered in 2005. Analysis of its internal motion indicates that it may contain a large amount of dark matter, as much as a small galaxy. Since VIRGOHI21 apparently c ...

in the Virgo cluster of galaxies), after the Boötes Dwarf (absolute magnitude −5.7) and the more recently discovered

Ursa Major II Dwarf Ursa Major II Dwarf (UMa II dSph) is a dwarf spheroidal galaxy situated in the Ursa Major constellation and discovered in 2006 in the data obtained by the Sloan Digital Sky Survey. The galaxy is located approximately 30 kpc from the Sun and m ...

(absolute magnitude −3.8). The

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

of the galaxy is estimated to be only −6.75, meaning that it is less luminous than some

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s, like

Deneb Deneb () is a first-magnitude star in the constellation of Cygnus, the swan. Deneb is one of the vertices of the asterism known as the Summer Triangle and the "head" of the Northern Cross. It is the brightest star in Cygnus and the ...

in the Milky Way. It is comparable in luminosity to Rigel. It has been described as similar to the Sextans Dwarf Galaxy. Both galaxies are ancient and metal-deficient. It estimated to be located at a distance of about 330,000

s (100 kpc) from the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. That is about twice the distance to the

Large Magellanic Cloud The Large Magellanic Cloud (LMC), or Nubecula Major, is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (≈160,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the ...

; the largest and most luminous satellite galaxy of the Milky Way.

Related objects

There was another object called "Ursa Major Dwarf", discovered by

Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an Americans, American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology. Hubble proved that many objects ...

in 1949. It was designated as

Palomar 4 Palomar 4 is a globular cluster of the Milky Way galaxy belonging to the Palomar Globular Clusters group. It was discovered in 1949 by Edwin Hubble and again in 1955 by A. G. Wilson. Based on measurements of the stars from the Gaia spacecraft, ...

. 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. The

was discovered in 2006 in the Ursa Major constellation and is also extraordinarily dim.

References

External links

* {{Sky, 10, 34, 52.8, +, 51, 55, 12, 330000 Dwarf spheroidal galaxies Local Group Milky Way Subgroup Ursa Major (constellation) ?

Discovery

Properties

Related objects

See also

References

External links