|Segue 2 Dwarf Galaxy|
|Observation data (J2000 epoch)|
|Right ascension||02h 19m 16s|
|Declination||+20° 10′ 31″|
|Distance||114 kly (35 kpc)|
|Apparent magnitude (V)||15.2 ± 0.2|
|Mass/Light ratio||650 M☉/L☉|
|Apparent size (V)||6.8+0.4|
Segue 2 is a dwarf spheroidal galaxy situated in the constellation Aries and discovered in 2009 in the data obtained by Sloan Digital Sky Survey. The galaxy is located at the distance of about 35 kpc (35,000 parsecs (110,000 ly)) 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.
The name is due to the fact that it was found by the SEGUE program, the Sloan Extension for Galactic Understanding and Exploration.
Segue 2 is one of the smallest and faintest satellites[note 1] 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 clusters. 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 [Fe/H] < −2, 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.
Circa 1,000 stars are supposed to exist within the galaxy.
- "NAME Segue 2". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-08-24.
- Belokurov, V.; Walker, M.G.; Evans, N.W.; et al. (2009). "Segue 2: A Prototype of the Population of Satellites of Satellites". Mon. Not. R. Astron. Soc. 397 (4): 1748–1755. arXiv:0903.0818. Bibcode:2009MNRAS.397.1748B. doi:10.1111/j.1365-2966.2009.15106.x.
- Martin, Nicolas F.; de Jong, Jelte T. A.; Rix, Hans-Walter (2008). "A Comprehensive Maximum Likelihood Analysis of the Structural Properties of Faint Milky Way Satellites". The Astrophysical Journal. 684 (2): 1075–1092. arXiv:0805.2945. Bibcode:2008ApJ...684.1075M. doi:10.1086/590336.
- "The Smallest Galaxies In the Universe Have the Most Dark Matter". Forbes. 2 December 2015. Retrieved 8 April 2016.
- Kirby, Evan; Michael Boylan-Kolchin; Judith G. Cohen; Marla Geha; James S. Bullock; Manoj Kaplinghat (June 10, 2013). "Segue 2: The Least Massive Galaxy" (PDF). The Astrophysical Journal. arXiv:1304.6080. Bibcode:2013ApJ...770...16K. doi:10.1088/0004-637X/770/1/16.
Megan Gannon (2013-06-10). "Dwarf Galaxy Segue 2 Called Smallest Ever Discovered". Huffington Post. Retrieved 2013-06-23.
The dwarf galaxy known as Segue 2 is bound together by a tiny clump of dark matter. Scientists who measured it using Hawaii's Keck Observatory say the finding adds support to theories about the formation of the universe.
- UCI Scientists Size Up Universe’s Most Lightweight Dwarf Galaxy with Keck Observatory Steve Steve, W. M. Keck Observatory updated June 7, 2013
- Bryan Nelson (11 June 2013). "Just how big is the smallest galaxy in the universe?". Mother Nature Network. Retrieved 8 April 2016.
| Least massive galaxy known