Arches Cluster

Arches Cluster

Arches Cluster of young, massive stars. This image was obtained with NACO adaptive optics system on ESO’s Very Large Telescope.
Observation data (J2000 epoch)
Constellation Sagittarius
Right ascension 17h 45m 50.5s
Declination –28° 49′ 28″
Distance 25 kly (8.5 kpc)
Physical characteristics
Notable features Optically obscured
Arches Cluster NASA/ESA Hubble Space Telescope 5/29/2015 Infrared image

The Arches Cluster is the densest known star cluster in the Milky Way located about 100 light years from its center, in the constellation Sagittarius (The Archer), 25,000 light-years from Earth. The discovery of this cluster was reported by Nagata et al. in 1995,[1] and independently by Cotera et al. in 1996.[2] Due to extremely heavy optical extinction by dust in this region, the Arches Cluster is obscured in the visual bands, and is observed in the X-ray, infrared, and radio bands. It contains approximately 135 young, very hot stars that are many times larger and more massive than the Sun, plus many thousands of less massive stars.[3]

This star cluster is estimated to be around two and a half million years old.[3] Although larger and denser than the nearby Quintuplet Cluster, it appears to be slightly younger. The most evolved stars are barely edging away from the main sequence while the Quintuplet Cluster includes a number of hot supergiants as well as a red supergiant and three Luminous Blue Variables.

Work by Donald Figer, an astronomer at the Rochester Institute of Technology suggests that 150 solar masses (M☉) is the upper limit of stellar mass in the current era of the universe. He used the Hubble Space Telescope to observe about a thousand stars in the Arches cluster and found no stars over that limit despite a statistical expectation that there should be several.[4] However, later research demonstrated a very high sensitivity of the calculated star masses upon the extinction laws used for mass derivation, which can affect the upper mass limit by about 30% using different extinction laws[5] (possibly from 150 M☉ to about 100 M☉).

Prominent stars
Star (B=Blum,[6] F=Figer[7]) Spectral type[8] Magnitude[8] (bolometric) Temperature[8] (effective, K) Mass[9] (M☉) Radius (R☉)
B1 WN8-9h −10.1 31,700 50 - 60 32
F1 WN8-9h −11.0 33,200 101 - 119 43
F2 WN8-9h −10.2 33,500 42 - 49 30
F3 WN8-9h −10.5 29,600 52 - 63 43
F4 WN7-8h −11.0 36,800 66 - 76 35
F5 WN8-9h −10.1 32,100 31 - 36 31
F6 WN8-9h −11.1 33,900 101 - 119 44
F7 WN8-9h −11.0 32,900 86 - 102 44
F8 WN8-9h −10.5 32,900 43 - 51 35
F9 WN8-9h −11.1 36,600 111 - 131 38
F10 O4-6If+ −10.1 32,200 55 - 69 24
F12 WN7-8h −10.8 36,900 70 - 82 31
F14 WN8-9h −10.2 34,500 54 - 65 28
F15 O4-6If+ −10.6 35,600 80 - 97 32
F16 WN8-9h −10.0 32,200 46 - 56 29
F18 O4-6I −10.4 36,900 67 - 82 26
F20 O4-6I −10.0 38,200 47 - 57 21
F21 O4-6I −10.1 35,500 56 - 70 25
F28 O4-6I −10.1 39,600 57 - 72 23

References

  1. ↑ Nagata, T.; Woodward, C.; Shure, M.; Kobayashi, N. (April 1995). "Object 17: Another cluster of emission-line stars near the Galactic center". Astronomical Journal 109 (4): 1676. Bibcode:1995AJ....109.1676N. doi:10.1086/117395.
  2. ↑ Cotera, A.; Erickson, E.; Colgan, S.; Simpson, J.; Allen, D.; Burton, M. (April 1996). "The discovery of hot stars near the Galactic center thermal radio filaments". Astrophysical Journal 461 (750): 750. Bibcode:1996ApJ...461..750C. doi:10.1086/177099.
  3. 1 2 Espinoza, P.; Selman3, F. J.; Melnick, J. (July 2009). "The massive star initial mass function of the Arches cluster". Astronomy and Astrophysics 504 (2): 563–583. arXiv:0903.2222. Bibcode:2009A&A...501..563E. doi:10.1051/0004-6361/20078597.
  4. ↑ Figer, Donald F. (2005). "An upper limit to the masses of stars". Nature 434 (7030): 192–194. arXiv:astro-ph/0503193. Bibcode:2005Natur.434..192F. doi:10.1038/nature03293. ISSN 0028-0836. PMID 15758993.
  5. ↑ Habibi, M.; Stolte, A.; Brandner, W.; Hußmann, B.; Motohara, K. (August 2013). "The Arches cluster out to its tidal radius: dynamical mass segregation and the effect of the extinction law on the stellar mass function". Astronomy and Astrophysics 556 (A26): A26. arXiv:1212.3355. Bibcode:2013A&A...556A..26H. doi:10.1051/0004-6361/201220556.
  6. ↑ Blum, R. D.; Schaerer, D.; Pasquali, A.; Heydari-Malayeri, M.; Conti, P. S.; Schmutz, W. (2001). "2 Micron Narrowband Adaptive Optics Imaging in the Arches Cluster". The Astronomical Journal 122 (4): 1875. arXiv:astro-ph/0106496. Bibcode:2001AJ....122.1875B. doi:10.1086/323096.
  7. ↑ Figer, D. F.; Najarro, F.; Gilmore, D.; Morris, M.; Kim, S. S.; Serabyn, E.; McLean, I. S.; Gilbert, A. M.; Graham, J. R.; Larkin, J. E.; Levenson, N. A.; Teplitz, H. I. (2002). "Massive Stars in the Arches Cluster". The Astrophysical Journal 581: 258. arXiv:astro-ph/0208145. Bibcode:2002ApJ...581..258F. doi:10.1086/344154.
  8. 1 2 3 Martins, F.; Hillier, D. J.; Paumard, T.; Eisenhauer, F.; Ott, T.; Genzel, R. (2008). "The most massive stars in the Arches cluster". Astronomy and Astrophysics 478: 219. arXiv:0711.0657. Bibcode:2008A&A...478..219M. doi:10.1051/0004-6361:20078469.
  9. ↑ Gräfener, G.; Vink, J. S.; de Koter, A.; Langer, N. (2011). "The Eddington factor as the key to understand the winds of the most massive stars". Astronomy & Astrophysics 535: A56. arXiv:1106.5361. Bibcode:2011A&A...535A..56G. doi:10.1051/0004-6361/201116701. ISSN 0004-6361.

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