R136a2

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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
Observation data
Epoch J2000      Equinox J2000
Constellation Dorado
Right ascension 05h 38m 42.40s[1]
Declination −69° 06′ 02.88″[1]
Apparent magnitude (V) 12.34[1]
Characteristics
Evolutionary stage
Wolf-Rayet star
Spectral type WN5h[2]
B−V color index 0.23[1]
Distance
163,000 ly
(50,000[3] pc)
Absolute magnitude (MV)-7.80[4]
Absolute bolometric
magnitude (Mbol)		-12.0[5]
Details
Myr
BAT99
 109, CHH92 2
Database references
SIMBADdata

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 151 M☉ and 3.5 million L☉
respectively.

Discovery

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.[8]

In the early 1980s,

speckle interferometry into 8 components.[9] 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[10] had led to speculation that a star several thousand times the mass of the sun was the more likely explanation.[11] Instead it was eventually found that it consisted of a few extremely luminous stars accompanied by a larger number of hot O stars.[1]

Distance

Main article: Large Magellanic Cloud § Distance

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.[3]

Properties

Like all Wolf-Rayet stars, R136a2 is undergoing severe mass loss by a fast stellar wind. The star loses 4.6×10−5 solar masses per year through a stellar wind with a speed of 2,400 km/s.[5][12] The high mass of the star compresses and heats the core and promotes rapid hydrogen fusion predominantly through the CNO process, leading to a luminosity of 5,129,000 L☉. The fusion rate is so great that in 10 seconds R136a2 produces more energy than the Sun does in a year. It may have been a 221 M☉ star at the time it was born and lost as much as 24 M☉ in the past 1 to 2 million years,[4] but since current theories suggest that no stars can be born above 150 M☉ it may be a merger of two or more stars.[13]

Although the star is one of the

VY CMa. Because of the high temperature, it emits most of its energy in the ultraviolet region of the electromagnetic spectrum, and the visual brightness is only 114,000 times the sun (MV −7.80).[4]

Fate

Main articles: Stellar evolution and Supernova

It is thought that stars this massive can never lose enough mass to avoid a catastrophic end with the collapse of a large iron core. The result will be a

Gamma ray bursts are only expected under unusual conditions, or for less massive stars.[14]

References

  1. ^
    S2CID 118510909
    .
  2. S2CID 11425847
    .
  3. ^
    S2CID 4417699
    .
  4. ^
    doi:10.1093/mnras/staa2801
    .
  5. ^
    S2CID 55123954
    .
  6. S2CID 247025548
    .
  7. S2CID 251067072
    .
  8. doi:10.1093/mnras/121.4.337
    .
  9. Bibcode:1985A&A...150L..18W
    .
  10. Bibcode:1983A&A...125...83M
    .
  11. PMID 17790538
    .
  12. S2CID 53001712
    .
  13. S2CID 119202197
    .
  14. S2CID 119238749
    .

External links
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