Canes Venatici I or CVn I is a

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 to systems that are comp ...

situated in the

Canes Venatici Canes Venatici () is one of the IAU designated constellations, 88 constellations designated by the International Astronomical Union (IAU). It is a small northern constellation that was created by Johannes Hevelius in the 17th century. Its name is ...

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

and discovered in 2006 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 ...

. It is one of the most distant known satellites of 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 ...

as of 2011 together with

Leo I The LEO I (Lyons Electronic Office I) was the first computer used for commercial business applications. The prototype LEO I was modelled closely on the Cambridge EDSAC. Its construction was overseen by Oliver Standingford, Raymond Thompson and D ...

and Leo II. The galaxy is located at a distance of about 220 kpc from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

and is moving away from the Sun at a velocity of about 31 km/s. It is classified as a

(dSph) meaning that it has an elliptical (ratio of axes ~ 2.5:1) shape with the half-light radius of about 550 pc. CVn I is a relatively faint satellite of the Milky Way—its integrated luminosity is about 230,000 times that of the Sun (absolute

visible magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of about −8.6). However, its mass is about 27 million

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

es, which means that the galaxy's

mass to light ratio In astrophysics and physical cosmology the mass-to-light ratio, normally designated with the Greek letter upsilon, , is the quotient between the total mass of a spatial volume (typically on the scales of a galaxy or a cluster) and its luminosity ...

is around 220. A high mass to light ratio implies that CVn I is dominated by the

dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

. The stellar population of CVn I consists mainly of old stars formed more than 10 billion years ago. The metallicity of these old stars is also very low at , which means that they contain 110 times less heavy elements than the Sun. There are also about 60

RR Lyrae RR Lyrae is a variable star in the Lyra constellation, figuring in its west near to Cygnus. As the brightest star in its class, it became the eponym for the RR Lyrae variable class of stars and it has been extensively studied by astro ...

stars. The galaxy also contains a small fraction of younger (1–2 billion years old) more metal-rich () stars, which account for about 5% of its mass and 10% of its light. These younger stars are concentrated in the center of the galaxy. There is currently no star formation in CVn I and the measurements have so far failed to detect

neutral hydrogen The hydrogen line, 21 centimeter line, or H I line is the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation has a precise frequency of , w ...

in it—the upper limit is 30,000 solar masses.

References

External links

The Universe within 500000 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 {{DEFAULTSORT:Dwarf galaxy, Canes Venatici I Dwarf spheroidal galaxies Local Group Milky Way Subgroup Canes Venatici 4689223 ?