Segue 2 (dwarf galaxy)
Encyclopedia
Segue 2 is a dwarf spheroidal galaxy
situated in the Aries constellation and discovered in 2007 in the data obtained by Sloan Digital Sky Survey
. The galaxy is located at the distance of about 35 kpc from the Sun and moves towards the Sun with the speed of 40 km/s. It is classified as a dwarf spheroidal galaxy
(dSph) meaning that it has an approximately round shape with the half-light radius
of about 34 pc.
Segue 2 is one of the smallest and faintest satellites of the Milky Way
—its integrated luminosity is about 800 times that of the Sun (absolute visible magnitude of about −2.5), which is much lower than the luminosity of the majority of globular cluster
s. However the mass of the galaxy—about 550,000 solar masses—is substantial, corresponding to the mass to light ratio
of about 650.
The stellar population of Segue 2 consists mainly of old stars formed more than 12 billion years ago. The metallicity of these old stars is also very low at , which means that they contain at least 100 times less heavy elements than the Sun. The stars of Segue 2 were probably among the first stars to form in the Universe
. Currently there is no star formation in Segue 2.
Segue 2 is located near the edge of Sagittarius stream
and at the same distance. It may once have been a satellite of Sagittarius Dwarf Elliptical Galaxy
or its star cluster.
Dwarf spheroidal galaxy
Dwarf spheroidal galaxy is a term in astronomy applied to low luminosity galaxies that are companions to the Milky Way and to the similar systems that are companions to the Andromeda Galaxy M31...
situated in the Aries constellation and discovered in 2007 in the data obtained by Sloan Digital Sky Survey
Sloan Digital Sky Survey
The Sloan Digital Sky Survey or SDSS is a major multi-filter 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 was named after the Alfred P...
. The galaxy is located at the distance of about 35 kpc from the Sun and moves towards the Sun with the speed of 40 km/s. It is classified as a dwarf spheroidal galaxy
Dwarf spheroidal galaxy
Dwarf spheroidal galaxy is a term in astronomy applied to low luminosity galaxies that are companions to the Milky Way and to the similar systems that are companions to the Andromeda Galaxy M31...
(dSph) meaning that it has an approximately round shape with the half-light radius
Effective radius
The effective radius of a galaxy is the radius at which one half of the total light of the system is emitted interior to this radius. This assumes the galaxy is circularly symmetric...
of about 34 pc.
Segue 2 is one of the smallest and faintest satellites of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
—its integrated luminosity is about 800 times that of the Sun (absolute visible magnitude of about −2.5), which is much lower than the luminosity of the majority of globular cluster
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
s. However the mass of the galaxy—about 550,000 solar masses—is substantial, corresponding to the mass to light ratio
Mass to light ratio
In astrophysics and physical cosmology the mass to light ratio, normally designated with the symbol \Upsilon is the quotient between the total mass of a spatial volume and its luminosity...
of about 650.
The stellar population of Segue 2 consists mainly of old stars formed more than 12 billion years ago. The metallicity of these old stars is also very low at , which means that they contain at least 100 times less heavy elements than the Sun. The stars of Segue 2 were probably among the first stars to form in the Universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
. Currently there is no star formation in Segue 2.
Segue 2 is located near the edge of Sagittarius stream
Field of Streams
The Field of Streams is a patch of sky where several stellar streams are visible and crisscross. The analysis of the streams of the zone determined that the dark matter configuration of the Milky Way Galaxy in the inner halo is round, at variance with expectations that it would be oblate.It was...
and at the same distance. It may once have been a satellite of Sagittarius Dwarf Elliptical Galaxy
Sagittarius Dwarf Elliptical Galaxy
The Sagittarius Dwarf Elliptical Galaxy is an elliptical loop-shaped satellite galaxy of the Milky Way Galaxy. It consists of four globular clusters, the main cluster being discovered in 1994...
or its star cluster.