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RSGC1 (Red Supergiant Cluster 1) is a young massive open cluster belonging to the Milky Way galaxy. It was discovered in 2006 in the data generated by several infrared surveys, named for the unprecedented number of red supergiant members.[3] The cluster is located in the constellation Scutum at the distance of about 6.6 kpc from the Sun. It is likely situated at the intersection of the northern end of the Long Bar of the Milky Way and the inner portion of the Scutum–Centaurus Arm—one of its two major spiral arms.[4]

Spitzer image of RSGC1
Observation data (J2000 epoch)
Right ascension18h 36m 29s[1]
Declination−06° 52′ 48″[1]
Distance22.0 ± 2.9kly (6.60 ± 0.89kpc[2])
Apparent magnitude (V)not visible[2]
Apparent dimensions (V)~1.5′[3][1]
Physical characteristics
Mass~3 × 104[2] M
Radius1.5 ± 0.3 pc[2]
Estimated age12 ± 2 my[2][1]
See also: Open cluster, List of open clusters

The age of RSGC1 is estimated at 10–14 million years. The cluster is heavily obscured and has not been detected in the visible light. It lies close to other groupings of red supergiants known as Stephenson 2, RSGC3 and Alicante 8. The mass of RSGC1 is estimated at 30 thousand solar masses, which makes it one of the most massive open clusters in the Galaxy.[2]

The observed red supergiants with the mass of about 16–20 solar masses are type II supernova progenitors.[2] Over 200 main sequence stars have been detected with masses over 8 M, which allows the distance to be determined from main sequence fitting. Fourteen red supergiant members have been identified.[1]

Prominent supergiants[2]
Star Spectral type Magnitude (K band) Temperature (effective, K) Absolute magnitude Luminosity (L)
F01 M5 4.962 3,450 −11.75 263,000
F02 M2 5.029 3,660 −11.92 363,000
F03 M5 5.333 3,450 −11.28 174,000
F04 M1 5.342 3,752 −11.24 209,000
F05 M4 5.535 3,535 −11.36 195,000
F06 M5 5.613 3,450 −10.70 100,000
F07 M3 5.631 3,605 −10.81 126,000
F08 M3 5.654 3,605 −11.33 200,000
F09 M6 5.670 3,399 −10.92 117,000
F10 M3 5.709 3,605 −10.86 132,000
F11 M5 5.722 3,535 −11.03 145,000
F12[3] M0 5.864 −10.70 200,000
F13 K2 5.957 4,015 −11.39 282,000
F14 M3 6.167 3,605 −10.25 74,000
F15 G0 6.682 6,850 −10.07 229,000


  1. 1.0 1.1 1.2 1.3 1.4 Froebrich, D.; Scholz, A. (2013). "The main sequence of three red supergiant clusters". Monthly Notices of the Royal Astronomical Society 436 (2): 1116–1122. arXiv:1308.6436. Bibcode 2013MNRAS.436.1116F. doi:10.1093/mnras/stt1633. ISSN 0035-8711.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Davies, B.; Figer, D. F.; Law, C. J.; Kudritzki, R. P.; Najarro, F.; Herrero, A.; MacKenty, J. W. (2008). "The Cool Supergiant Population of the Massive Young Star Cluster RSGC1". The Astrophysical Journal 676 (2): 1016–1028. arXiv:0711.4757. Bibcode 2008ApJ...676.1016D. doi:10.1086/527350.
  3. 3.0 3.1 3.2 Figer, D. F.; MacKenty, J. W.; Robberto, M.; Smith, K.; Najarro, F.; Kudritzki, R. P.; Herrero, A. (2006). "Discovery of an Extraordinarily Massive Cluster of Red Supergiants". The Astrophysical Journal 643 (2): 1166–1179. arXiv:astro-ph/0602146. Bibcode 2006ApJ...643.1166F. doi:10.1086/503275.
  4. Davies, B.; Figer, D. F.; Kudritzki, R. P.; MacKenty, J.; Najarro, F.; Herrero, A. (2007). "A Massive Cluster of Red Supergiants at the Base of the Scutum‐Crux Arm". The Astrophysical Journal 671: 781. arXiv:0708.0821. Bibcode 2007ApJ...671..781D. doi:10.1086/522224.

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