Reticulum II
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Reticulum II (or Reticulum 2) is a dwarf galaxy in the Local Group. Reticulum II was discovered in 2015 by analysing images from the Dark Energy Survey. It is a satellite of the Magellanic Clouds and was probably captured relatively recently.[3] Like other dwarf spheroidal galaxies, its stellar population is old: the galaxy was quenched before 11.5 billion years ago.[3]
| Reticulum II | |
|---|---|
| Observation data (J2000 epoch) | |
| Constellation | Reticulum |
| Right ascension | 03h 35m 42.14s[1] |
| Declination | −54° 2′ 57.1″[1] |
| Distance | 103 kly (31.6 kpc)[2] |
| Apparent magnitude (V) | 17.4[1] |
| Characteristics | |
| Apparent size (V) | 3.37′ × 3.64′[1] |
| Notable features | Enriched in r-process elements |
| Other designations | |
| Reticulum II, Reticulum 2[1] | |
Reticulum II is elongated, having a major/minor axis ratio of 0.6. The size is given by a half-light radius of 15 parsecs (pc). This is too large for it to be a globular cluster. The absolute magnitude (MV) of the galaxy is −2.7. The distance from Earth is about 30 kpc.[2] The galaxy contains some blue horizontal branch stars. Other features visible are a main sequence, and a main sequence turn off, and a red giant branch.[1][4] It has an unusual enhancement of r-process elements, meaning that gold and europium are enriched in the brightest stars in the galaxy.[5] About 72% of its stars are enriched in r-process elements.[2] The implication of the unusual enrichment in elements heavier than zinc, is that the r-process is very rare, and only happened once in this galaxy, possibly by the collision of two neutron stars.[6]
Gamma rays mostly with energies between 2 and 10 GeV have been detected by the Fermi satellite.[7] The radiation from Reticulum II is more significant than that of other dwarf galaxy emissions.[8] However this finding has been contested.[9]
It has been named as a "globular-cluster-like dwarf".[10]