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.
 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] |
| Astrometry | |
| Distance | 163,000 ly (50,000[3] pc) |
| Absolute magnitude (MV) | -7.80[4] |
| Absolute bolometric magnitude (Mbol) | -12.0[5] |
| Details[6][7] | |
| Mass | 151+27 −16 M☉ |
| Radius | 25.2+4.1 −3.5 R☉ |
| Luminosity | 3,548,000 L☉ |
| Temperature | 50,000 K |
| Rotational velocity (v sin i) | 150 km/s |
| Age | 1.34+0.13 −0.18 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Discovery
editIn 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, R136a was first resolved using 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
editDetermining 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
editLike 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 most massive known it has a radius of 34.7 R☉ and a volume of 41,800 suns,[4] 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 114,000 times the sun (MV −7.80).[4]
Fate
editIt 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. 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.[14]
References
edit- ^ a b c d e 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. arXiv:1308.3412. Bibcode:2013A&A...558A.134D. doi:10.1051/0004-6361/201321824. S2CID 118510909.
- ^ 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. arXiv:0905.2934. Bibcode:2009MNRAS.397.2049S. doi:10.1111/j.1365-2966.2009.15060.x. S2CID 11425847.
- ^ 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): 76–9. arXiv:1303.2063. Bibcode:2013Natur.495...76P. doi:10.1038/nature11878. PMID 23467166. S2CID 4417699.
- ^ a b c d Bestenlehner, Joachim M.; Crowther, Paul A.; Caballero-Nieves, Saida M.; Schneider, Fabian R. N.; Simón-Díaz, Sergio; Brands, Sarah A.; De Koter, Alex; Gräfener, Götz; Herrero, Artemio; Langer, Norbert; Lennon, Daniel J.; Maíz Apellániz, Jesus; Puls, Joachim; Vink, Jorick S. (2020). "The R136 star cluster dissected with Hubble Space Telescope/STIS. II. Physical properties of the most massive stars in R136". Monthly Notices of the Royal Astronomical Society. 499 (2): 1918. arXiv:2009.05136. Bibcode:2020MNRAS.499.1918B. doi:10.1093/mnras/staa2801.
- ^ a b 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. arXiv:1401.5474. Bibcode:2014A&A...565A..27H. doi:10.1051/0004-6361/201322696. S2CID 55123954.
- ^ Brands, S.; de Koter, A.; Bestenlehner, J.; Crowther, P.; Sundqvist, J.; Puls, J.; Caballero-Nieves, S.; Abdul-Masih, M.; Driessen, F.; Garcia, M.; Geen, S.; Gräfener, G.; Hawcroft, C.; Kaper, L.; Keszthelyi, Z.; Langer, N.; Sana, H.; Schneider, Fabian R. N.; Shenar, T.; Vink, Jorick S. (7 April 2022). "The R136 star cluster dissected with Hubble Space Telescope/STIS. III. The most massive stars and their clumped winds". Astronomy & Astrophysics. 663: A36. arXiv:2202.11080. Bibcode:2022A&A...663A..36B. doi:10.1051/0004-6361/202142742. ISSN 0004-6361. S2CID 247025548.
- ^ Kalari, Venu M.; Horch, Elliott P.; Salinas, Ricardo; Vink, Jorick S.; Andersen, Morten; Bestenlehner, Joachim M.; Rubio, Monica (2022-07-26). "Resolving the Core of R136 in the Optical". The Astrophysical Journal. 935 (2): 162. arXiv:2207.13078. Bibcode:2022ApJ...935..162K. doi:10.3847/1538-4357/ac8424. S2CID 251067072.
- ^ 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 (4): 337. Bibcode:1960MNRAS.121..337F. doi:10.1093/mnras/121.4.337.
- ^ Weigelt, G.; Baier, G. (1985). "R136a in the 30 Doradus nebula resolved by holographic speckle interferometry". Astronomy and Astrophysics. 150: L18. Bibcode:1985A&A...150L..18W.
- ^ Moffat, A. F. J.; Seggewiss, W. (1983). "R136 - Supermassive star or dense core of a star cluster?". Astronomy and Astrophysics. 125: 83. Bibcode:1983A&A...125...83M.
- ^ Cassinelli, J. P.; Mathis, J. S.; Savage, B. D. (1981). "Central Object of the 30 Doradus Nebula, a Supermassive Star". Science. 212 (4502): 1497–501. Bibcode:1981Sci...212.1497C. doi:10.1126/science.212.4502.1497. PMID 17790538.
- ^ 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. arXiv:1007.3284. Bibcode:2010MNRAS.408..731C. doi:10.1111/j.1365-2966.2010.17167.x. S2CID 53001712.
- ^ 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. arXiv:1208.0826. Bibcode:2012MNRAS.426.1416B. doi:10.1111/j.1365-2966.2012.21672.x. S2CID 119202197.
- ^ Woosley, Stan. E.; Heger, Alexander (2015). "The Deaths of Very Massive Stars". Very Massive Stars in the Local Universe. Astrophysics and Space Science Library. Vol. 412. pp. 199–225. arXiv:1406.5657. Bibcode:2015ASSL..412..199W. doi:10.1007/978-3-319-09596-7_7. ISBN 978-3-319-09595-0. S2CID 119238749.