RSGC1

RSGC1 (Red Supergiant Cluster 1) is a young massive open cluster in 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. 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.

The age of RSGC1 is estimated at 10–14 million years. The cluster is heavily obscured and has not been detected in visible light. It lies close to other groupings of red supergiants known as Stephenson 2, RSGC3, Alicante 7, Alicante 8, and Alicante 10. The mass of RSGC1 is estimated at 30 thousand solar masses, which makes it one of the most massive open clusters in the Galaxy.

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

RSGC1-F01
RSGC1-F01 is a red supergiant located in RSGC1. The radius was calculated to be around 1,450 -1,530 times that of the Sun (the radius is calculated by applying the Stefan-Boltzmann law), making it one of the largest stars discovered so far. This corresponds to a volume 3.58 billion times bigger than the Sun. If placed at the center of the Solar System, the photosphere would engulf the orbit of Jupiter.

RSGC1-F02
RSGC1-F02 is a red supergiant located in the RSGC1. Its radius was calculated to be between 1,499 and 1,549 or 1,128 times that of the Sun (the radius is calculated applying the Stefan-Boltzmann law), making it one of the largest stars discovered so far. This corresponds to a volume 3.37 and 3.72 billion times bigger than the Sun. If placed at the center of the Solar System, its photosphere would engulf the orbit of Jupiter.

RSGC1-F13
RSGC1-F13 is a peculiar red supergiant which is unusually red compared to the other stars. It is notable for having the highest mass-loss rate in the cluster at /yr. The star also has detected masers of SiO, H2O, and OH. ALMA detects CO emission in F13 along with four other supergiants in the cluster extending hundreds of stellar radii away from the stars. The CO mass loss rate is estimated to be /yr, which is an order of magnitude larger than the predicted value for the other red supergiants in the study. F13 is compared with VY Canis Majoris as a similarly extreme red supergiant, both displaying stronger and possibly eruptive mass-loss.