Segue 2
| Segue 2 Dwarf Galaxy[1] | |
|---|---|
| Observation data (J2000 epoch) | |
| Constellation | Aries |
| Right ascension | 02h 19m 16s[1] |
| Declination | +20° 10′ 31″[1] |
| Distance | 114 kly (35 kpc)[2] |
| Type | dSph[2] |
| Mass | 5.5×105[2] M☉ |
| Mass/Light ratio | 650[2] M☉/L☉ |
| Apparent dimensions (V) | 6.8+0.4 −0.4′[2] |
| Apparent magnitude (V) | 15.2 ± 0.2[2] |
| Other designations | |
| Segue 2[2] | |
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.[2] 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.[2] 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.[2]
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.[2] However, the mass of the galaxy—about 550,000 solar masses—is substantial, corresponding to the mass to light ratio of about 650.[2]
The stellar population of Segue 2 consists mainly of old stars formed more than 12 billion years ago.[2] 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.[2] 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.[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.[2]
In June 2013 the The Astrophysical Journal reported that Segue 2 was bound together with dark matter.[4][5][6]
Notes
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<references />, or <references group="..." />| Preceded by | Least massive galaxy known 2013 — 150,000MSun |
Succeeded by incumbent |
| Location |
Milky Way → Milky Way subgroup → Local Group → Virgo Supercluster → Laniakea Supercluster → Observable universe → Universe
Each arrow (→) may be read as "within" or "part of". |
 |
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|---|---|---|---|---|---|---|---|---|---|
| Galactic core | |||||||||
| Spiral arms | |||||||||
| Satellite galaxies |
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| Related | |||||||||
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- ↑ UCI Scientists Size Up Universe’s Most Lightweight Dwarf Galaxy with Keck Observatory Steve Steve, W. M. Keck Observatory updated June 7, 2013
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