Segue 2

Segue 2 is a spheroidal dwarf galaxy ( dSph ) in the constellation of Aries. She was discovered in 2007 after analysis of the data of the survey of the Sloan Digital Sky Survey. The galaxy is at a distance of about 35 kpc to the solar system and has a heliocentric radial velocity of -40 km / s. It has an approximately circular shape and a very small dwarf galaxies for the half-light radius of only 34 pc.

Properties

Segue 2 is the smallest and faintest satellites (Only Segue 1 and Willman 1 are still fainter ) of the Milky Way. The integral luminosity is only 800 L ☉ with an absolute magnitude of MV = -2.5 likes, which is significantly less than that of the majority of globular clusters. Nevertheless, the mass of the galaxy about 550,000 M ☉ is leading to a mass -luminosity ratio of 650.

The stellar population of Segue 2 consists mainly of older stars, which emerged more than 12 billion years ago. Thus, they are probably the first stars ever to have formed in the universe. Work is currently Segue 2 no relevant star formation observed.

The metallicity is correspondingly low, with a value of [Fe / H] < -2, which is equivalent to the fact that it at least 100 times less in heavy elements than the Sun has.

Segue 2 is located near the edge of the Sagittarius stream and also at about the same distance to the solar system. Maybe it was once a satellite of the Sagittarius dwarf galaxy or one of its globular clusters.