R136a2
 The central region of the R136 star cluster as seen in near infrared. R136a1 and R136a2 are the two very close bright stars at the center, with R136a2 being the fainter of the two. Credit: ESO |
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| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Dorado |
| Right ascension | 05h 38m 42.40s |
| Declination | −69° 06′ 02.88″ |
| Apparent magnitude (V) | 12.34 |
| Characteristics | |
| Evolutionary stage | Wolf-Rayet star |
| Spectral type | WN5h |
| B−V color index | 0.23 |
| Astrometry | |
| Distance | 163,000 ly (50,000pc) |
| Absolute magnitude (MV) | -7.52 |
| Absolute bolometric magnitude (Mbol) |
-12.0 |
| Details | |
| Mass | 195 M☉ |
| Radius | 23.4 R☉ |
| Luminosity | 4,266,000 L☉ |
| Luminosity (visual, LV) | 87,000 L☉ |
| Temperature | 53,000 K |
| Rotation | 200 km/s |
| Age | 0.3 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
R136a2 (RMC 136a2) is a Wolf-Rayet star residing near the center of the R136, the central concentration of stars of the large NGC 2070 open cluster in the Tarantula Nebula, a massive H II region in the Large Magellanic Cloud which is a nearby satellite galaxy of the Milky Way. It has one of the highest confirmed masses and luminosities of any known star, at about 195 M☉ and 4.3 million L☉ respectively.
In 1960, a group of astronomers working at the Radcliffe Observatory in Pretoria made systematic measurements of the brightness and spectra of bright stars in the Large Magellanic Cloud. Among the objects cataloged was RMC 136, (Radcliffe Observatory Magellanic Cloud Catalogue, Catalog number 136) the central "star" of 30 Doradus. Subsequent observations showed that R136 was located in the center of a giant H II region that was a center of intense star formation in the immediate vicinity of the observed stars.
In the early 1980s, R136a was first resolved using speckle interferometry into 8 components. R136a2 was marginally the second brightest found within 1 arc-second at the centre of the R136 cluster. Previous estimates that the brightness of the central region would require as many as 30 hot O class stars within half a parsec at the centre of the cluster had led to speculation that a star several thousand times the mass of the sun was the more likely explanation. Instead it was eventually found that it consisted of a few extremely luminous stars accompanied by a larger number of hot O stars.
Determining a precise distance to R136a2 is challenging due to many factors. At the immense distance to the LMC, the parallax method is beyond the limits of current technology. Most estimates assume that R136 is at the same distance as the Large Magellanic Cloud. The most accurate distance to the LMC is 49.97 kpc, derived from a comparison of the angular and linear dimensions of eclipsing binary stars.
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