R136a2

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R136a2
The young cluster R136.jpg
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 42.45s[1]
Declination −69° 06′ 02.2″[1]
Apparent magnitude (V) 12.34[2]
Characteristics
Evolutionary stage Wolf-Rayet star
Spectral type WN5h[3]
B−V color index 0.23[2]
Astrometry
Distance 163,000 ly
(50,000[4] pc)
Absolute magnitude (MV) -6.50[5]
Absolute bolometric
magnitude
 (Mbol)
-12.0[5]
Details
Mass 179[5] M
Radius 23.4[5] R
Luminosity 4,900,000[5] L
Luminosity (visual, LV) 32,000 L
Temperature 56,000[5] K
Metallicity ~0.4[citation needed]
Rotation 200 km/s[6]
Age ~1.7[6] Myr
Other designations
MH 511, RMC 136a2, HSH95 5, BAT99 109, CHH92 2
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 179 M and 4.9 million L respectively.

Discovery[edit]

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.[7]

In the early 1980s, R136a was first resolved using speckle interferometry into 8 components.[8] 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 [9] had led to speculation that a star several thousand times the mass of the sun was the more likely explanation.[10] Instead it was eventually found that it consisted of a few extremely luminous stars accompanied by a larger number of hot O stars.[2]

Distance[edit]

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.[4]

Properties[edit]

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 2400 km/s.[5][6] 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 4,900,000 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 240 M star at the time it was born and lost as much as 40 M in the past 1 to 2 million years,[6] but since current theories suggest that no stars can be born above 150 M it may be a merger of two or more stars.[11]

Although the star is one of the most massive known it has a radius of 23.4 R and a volume of 13,000 suns,[5] far smaller than the largest stars such as 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 32,000 times the sun (MV -6.5).[5]

Fate[edit]

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 supernova, hypernova, gamma-ray burst, or perhaps almost no visible explosion, and leaving behind a black hole or neutron star. The exact details depend heavily on the timing and amount of mass loss, with current models not fully reproducing the distribution of stars and supernovae that we observe. The most massive stars in the local universe are expected to progress to hydrogen-free Wolf Rayet stars before their cores collapse, producing a type Ib or Ic supernova and leaving behind a black hole. Gamma ray bursts are only expected under unusual conditions, or for less massive stars[12]

References[edit]

  1. ^ a b Breysacher, J.; Azzopardi, M.; Testor, G. (1999). "The fourth catalogue of Population I Wolf-Rayet stars in the Large Magellanic Cloud". Astronomy and Astrophysics Supplement 137: 117. Bibcode:1999A&AS..137..117B. doi:10.1051/aas:1999240. 
  2. ^ a b c Doran, E. I.; Crowther, P. A.; De Koter, A.; Evans, C. J.; McEvoy, C.; Walborn, N. R.; Bastian, N.; Bestenlehner, J. M.; Gräfener, G.; Herrero, A.; Köhler, K.; Maíz Apellániz, J.; Najarro, F.; Puls, J.; Sana, H.; Schneider, F. R. N.; Taylor, W. D.; Van Loon, J. Th.; Vink, J. S. (2013). "The VLT-FLAMES Tarantula Survey. XI. A census of the hot luminous stars and their feedback in 30 Doradus". Astronomy & Astrophysics 558: A134. Bibcode:2013A&A...558A.134D. doi:10.1051/0004-6361/201321824. 
  3. ^ Schnurr, O.; Chené, A.-N.; Casoli, J.; Moffat, A. F. J.; St-Louis, N. (2009). "VLT/SINFONI time-resolved spectroscopy of the central, luminous, H-rich WN stars of R136". Monthly Notices of the Royal Astronomical Society 397 (4): 2049. Bibcode:2009MNRAS.397.2049S. doi:10.1111/j.1365-2966.2009.15060.x. 
  4. ^ a b Pietrzyński, G.; Graczyk, D.; Gieren, W.; Thompson, I. B.; Pilecki, B.; Udalski, A.; Soszyński, I.; Kozłowski, S.; Konorski, P.; Suchomska, K.; Bono, G.; Moroni, P. G. Prada; Villanova, S.; Nardetto, N.; Bresolin, F.; Kudritzki, R. P.; Storm, J.; Gallenne, A.; Smolec, R.; Minniti, D.; Kubiak, M.; Szymański, M. K.; Poleski, R.; Wyrzykowski, Ł.; Ulaczyk, K.; Pietrukowicz, P.; Górski, M.; Karczmarek, P. (2013). "An eclipsing-binary distance to the Large Magellanic Cloud accurate to two per cent". Nature 495 (7439): 76. Bibcode:2013Natur.495...76P. doi:10.1038/nature11878. PMID 23467166. 
  5. ^ a b c d e f g h i Hainich, R.; Rühling, U.; Todt, H.; Oskinova, L. M.; Liermann, A.; Gräfener, G.; Foellmi, C.; Schnurr, O.; Hamann, W.-R. (2014). "The Wolf-Rayet stars in the Large Magellanic Cloud". Astronomy & Astrophysics 565: A27. Bibcode:2014A&A...565A..27H. doi:10.1051/0004-6361/201322696. 
  6. ^ a b c d Crowther, Paul A.; Schnurr, Olivier; Hirschi, Raphael; Yusof, Norhasliza; Parker, Richard J.; Goodwin, Simon P.; Kassim, Hasan Abu (2010). "The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 M⊙ stellar mass limit". Monthly Notices of the Royal Astronomical Society 408 (2): 731. Bibcode:2010MNRAS.408..731C. doi:10.1111/j.1365-2966.2010.17167.x. 
  7. ^ Feast, M. W.; Thackeray, A. D.; Wesselink, A. J. (1960). "The brightest stars in the Magellanic Clouds". Monthly Notices of the Royal Astronomical Society 121: 337. Bibcode:1960MNRAS.121..337F. 
  8. ^ Weigelt, G.; Baier, G. (1985). "R136a in the 30 Doradus nebula resolved by holographic speckle interferometry". Astronomy and Astrophysics (ISSN 0004- 6361) 150: L18. Bibcode:1985A&A...150L..18W. 
  9. ^ Moffat, A. F. J.; Seggewiss, W. (1983). "R136 - Supermassive star or dense core of a star cluster?". Astronomy and Astrophysics (ISSN 0004-6361) 125: 83. Bibcode:1983A&A...125...83M. 
  10. ^ Cassinelli, J. P.; Mathis, J. S.; Savage, B. D. (1981). "Central Object of the 30 Doradus Nebula, a Supermassive Star". Science 212 (4502): 1497. Bibcode:1981Sci...212.1497C. doi:10.1126/science.212.4502.1497. PMID 17790538. 
  11. ^ Banerjee, Sambaran; Kroupa, Pavel; Oh, Seungkyung (2012). "The emergence of super-canonical stars in R136-type starburst clusters". Monthly Notices of the Royal Astronomical Society 426 (2): 1416. Bibcode:2012MNRAS.426.1416B. doi:10.1111/j.1365-2966.2012.21672.x. 
  12. ^ Woosley, Stan. E.; Heger, Alexander (2015). "Very Massive Stars in the Local Universe". Very Massive Stars in the Local Universe. Astrophysics and Space Science Library 412: 199. Bibcode:2015ASSL..412..199W. doi:10.1007/978-3-319-09596-7_7. ISBN 978-3-319-09595-0.  |chapter= ignored (help)

External links[edit]