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, and independently by Cotera et al. in 1996. 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.

This star cluster is estimated to be around two and a half million years old. 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. 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 (possibly from 150 M_☉ to about 100 M_☉).

Prominent stars

Star (B=Blum, F=Figer)	Spectral type	Magnitude (bolometric)	Temperature (effective, K)	Mass (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

External links

• The Arches Cluster — ESO Image Gallery
• http://hubblesite.org/newscenter/newsdesk/archive/releases/1999/30/text/
• http://chandra.harvard.edu/photo/2001/arches/
• http://www.spaceimages.com/arstarclus.html