|Observation data (J2000 epoch)|
|Right ascension||17h 45m 50.5s|
|Declination||–28° 49′ 28″|
|Distance||25 kly (8.5 kpc)|
|Notable features||Optically obscured|
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. 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. The radius of the Arches Cluster is approximately one light-year. It contains approximately 150 young, very hot stars that are many times larger and more massive than the Sun. Such stars live for only a few million years before exhausting their hydrogen fuel, due to their extreme luminosity. The cluster also contains hot gas, produced in shocks by collisions among the massive, high-velocity stellar winds flowing outwards from the stars.
This star cluster and the Quintuplet cluster, another massive young cluster in the region, are estimated to be two to four million years old. Although possibly larger and denser than the 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 the Luminous Blue Variable The Pistol Star. The most massive of their stars are expected to become supernovas, forming neutron stars or black holes, or else be torn apart by tidal forces from the black hole known to lie at the Galactic center.
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. However, later research demonstrated a very high sensitivity of the calculated star masses upon the extiction laws used for mass derivation, which can affect the upper mass limit by about 30% using different extinction laws (possibly from 150 M☉ to about 100 M☉).
|Star (B=Blum, F=Figer)||Spectral type||Magnitude (bolometric)||Temperature (effective, K)||Mass (x solar)||Radius (x solar)|
|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|
- 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. Bibcode:2009A&A...501..563E. doi:10.1051/0004-6361/20078597. Retrieved 5 December 2014.
- "NASA's Hubble Weighs in on the Heaviest Stars in the Galaxy". NASA News. 2005-03-09. Retrieved 2006-08-04.
- 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). Bibcode:2013A&A...556A..26H. doi:10.1051/0004-6361/201220556. Retrieved 5 December 2014.
- 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.
- 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.
- 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.
- Gräfener; Vink; de Koter; Langer (2011). "The Eddington factor as the key to understand the winds of the most massive stars. Evidence for a Gamma-dependence of Wolf-Rayet type mass loss". arXiv:1106.5361v1 [astro-ph.SR].