R136a2

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R136a2 ( RMC 136a2 ) is a Wolf-Rayet star of type WN-5H in the star cluster R136 of the Tarantula Nebula , a massive H II region in the Large Magellanic Cloud .

The star R136a2 is located within the center of the open star cluster R136 in the cluster R136a. It has one of the highest confirmed masses and brightnesses among the known stars, at around 195 M ☉ and a luminosity of 4.3 million L ☉ .

The open star cluster R136 (consisting of the clusters R136 a, b and c). In the middle is the central cluster R136a with the stars a1-a24. The two brightest stars of the central cluster, R136a1 and R136a2, are in the center of the image and have just been resolved (with +/- 0.3 arc seconds). The second largest star R136a2 is immediately to the left of R136a1 and almost seems to be touching it. The distance is below 1/2 parsec ; however, R136a1 and R136a2 are not gravitationally bound. The third largest star R136c is at the bottom left, at the edge of the picture. It lies outside the central cluster in area c. In the central cluster there is also the fourth largest star R136a3, to the right below R136a1. The star R136b is located slightly above the connecting line between R136a1 and R136c) on the edge of the central cluster. It has a total mass of over 200 M ☉ and even exceeds R136a2 in mass. However, it is a multiple system with a central Wolf-Rayet star 93 M ☉.

It is also located in the immediate vicinity of the currently known, most mass-rich Wolf-Rayet star R136a1 (see figure on the right - > to the star cluster R136).

The star R136a2 exceeds - comparable to its neighboring stars R136a1 and 136c - the theoretical mass limit of 150 M ☉ , which stars could reach without a loss of stability (so-called "Eddington limit").

According to model calculations, this mass limit can be exceeded while maintaining the hydrodynamic equilibrium if B. merge two or more young, massive O-stars immediately in the main sequence evolution. Isolated HII regions offer a corresponding star density, including the star cluster R136. In this process of star merging, the maximum mass limit for stable stars according to model calculations is approx. 300 M ☉.

Physical background

R136a2 belongs to the type WN-5H. Stars in this spectral class (WN) have pronounced N emission lines due to the CNO cycle (Bethe-Weizsäcker cycle). In this context, the designation 5H means that the star's hydrogen content is high and the brazier (hydrogen to helium) extends deep into the star (so-called WNH stars).

When young 0-stars merge, massive stars can arise which exceed the limit of 150 M ☉ . These stars also have a pronounced stellar wind . The resulting young Wolf-Rayet stars of the WNH type show a disproportionately high increase in energy production. The background to this high energy production is the low metallicity of the stellar matter, accompanied by an intensive mixing of the fusing material. The intensive mixing is a side effect of the rapid rotation of the star.

The angular momentum of the star required for rapid rotation results directly from the orbital movements of the merging individual stars. With the aid of spectral analyzes and model calculations, it was possible to confirm these conditions for R136a1 and R136a2.

Future development

The high loss of mass is a constant feature of the Wolf-Rayet stars. The most luminous, hydrogen-richest Wolf-Rayet stars of the type WN-5H even lose most of their mass within only 2 - 3 million years (due to the stellar wind and excessive energy production). This is followed by the transition to type WNE ( low in hydrogen) and the start of helium burning.

Even before entering this phase, the speed of rotation is reduced many times over due to the stellar wind . At the transition to the WNE star, the remaining mass of the Wolf-Rayet star is below half of the original value. For R136a2 a mass of approx. 50 M ☉ and below is predicted for this point in time .

In the final stage, there is a high probability that R136a2 will become a type 1b or 1c supernova .

Web links

Individual evidence

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  3. ↑ WikiVisually.com. Retrieved July 3, 2020 .
  4. ^ MA Campbell, CJ Evans, AD Mackey, M. Gieles, J. Alves: VLT-MAD observations of the core of 30 Doradus . In: Monthly Notices of the Royal Astronomical Society . tape 405 , no. 1 , June 11, 2010, ISSN  0035-8711 , p. 421-435 , doi : 10.1111 / j.1365-2966.2010.16447.x ( oup.com [accessed July 2, 2020]).
  5. ^ MA Campbell, CJ Evans, AD Mackey, M. Gieles, J. Alves: VLT-MAD observations of the core of 30 Doradus . In: Monthly Notices of the Royal Astronomical Society . tape 405 , no. 1 , June 11, 2010, ISSN  0035-8711 , p. 421-435 , doi : 10.1111 / j.1365-2966.2010.16447.x ( oup.com [accessed July 2, 2020]).
  6. ↑ information@eso.org: Stars Just Got Bigger - A 300 Solar Mass Star Uncovered. Retrieved July 2, 2020 .
  7. ↑ n-tv NEWS: Astronomers crack secret. Retrieved July 7, 2020 .
  8. ↑ information@eso.org: Stars Just Got Bigger - A 300 Solar Mass Star Uncovered. Retrieved July 2, 2020 .
  9. ↑ WNH Stars . doi : 10.1086 / 586885 / fulltext / 72728.text.html ( iop.org [accessed July 5, 2020]).
  10. ↑ Sambaran Banerjee, Pavel Kroupa, Seungkyung Oh: The emergence of super-canonical stars in R136-type starburst clusters . In: Monthly Notices of the Royal Astronomical Society . tape 426 , no. 2 , October 2012, ISSN  0035-8711 , p. 1416–1426 , doi : 10.1111 / j.1365-2966.2012.21672.x ( harvard.edu [accessed July 7, 2020]).
  11. ↑ O. Schnurr, A.-N. Chené, J. Casoli, AFJ Moffat, N. St-Louis: VLT / SINFONI time-resolved spectroscopy of the central, luminous, H-rich WN stars of R136 . In: Monthly Notices of the Royal Astronomical Society . tape 397 , no. 4 , August 21, 2009, ISSN  0035-8711 , p. 2049–2056 , doi : 10.1111 / j.1365-2966.2009.15060.x ( oup.com [accessed July 2, 2020]).
  12. ↑ Cristina Chiappini, Urs Frischknecht, Georges Meynet, Raphael Hirschi, Beatriz Barbuy: Imprints of fast-rotating massive stars in the Galactic Bulge . In: nature . tape 472 , no. 7344 , April 2011, ISSN  0028-0836 , p. 454–457 , doi : 10.1038 / nature10000 ( harvard.edu [accessed July 2, 2020]).
  13. ^ Wolf-Rayet star . In: Academic Dictionaries and Encyclopedias . ( enacademic.com [accessed July 9, 2020]).
  14. ↑ Wolf-Rayet-Stern - Wolf – Rayet star - wiki.wiki. Retrieved July 5, 2020 .
  15. ^ EI Doran, PA Crowther, A. de Koter, CJ Evans, C. McEvoy: The VLT-FLAMES Tarantula Survey - XI. A census of the hot luminous stars and their feedback in 30 Doradus . In: Astronomy & Astrophysics . tape 558 , October 1, 2013, ISSN  0004-6361 , p. A134 , doi : 10.1051 / 0004-6361 / 201321824 ( aanda.org [accessed July 5, 2020]).
  16. ^ Wolf-Rayet star . In: Academic Dictionaries and Encyclopedias . ( enacademic.com [accessed July 5, 2020]).