Alicante 8, also known as RSGC4, (''Red Supergiant Cluster 4'') is an asterism, formerly thought to be a young massive

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

, belonging to the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

galaxy. It was discovered in 2010 in the

2MASS The Two Micron All-Sky Survey, or 2MASS, was an astronomical survey of the whole sky in infrared light. It took place between 1997 and 2001, in two different locations: at the U.S. Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona, and ...

survey data. As of 2010, the only members of the cluster that were identified are 8–13

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelg ...

s—young massive stars undergoing

helium burning The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon. In stars Helium accumulates in the cores of stars as a result of the proton–proton chain reaction a ...

in their cores. The cluster is located in the constellation Scutum at a distance of about 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 The Scutum–Centaurus Arm, also known as Scutum-Crux arm, is a long, diffuse curving streamer of stars, gas and dust that spirals outward from the proximate end of the Milky Way's central bar. The Milky Way has been posited since the 1950s to h ...

—one of the two major spiral arms. The age of Alicante 8 is estimated to be around 16–20 million years. The observed red supergiants are

type II supernova A Type II supernova or SNII (plural: ''supernovae'') results from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun () to undergo this type ...

progenitors. The cluster is heavily obscured and has not been detected in the

visible light Light, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400–700 nanometres (nm ...

. It lies close to other groupings of red supergiants known as RSGC1, Stephenson 2, RSGC3, Alicante 7, and Alicante 10. The mass of the open cluster is estimated at 10–20 thousand solar masses, which makes it one of the most massive open clusters in the Galaxy. A 2023 study of the radial velocities of the stars of Alicante 8 showed that they vary widely, instead of being similar as would be expected for a gravitationally bound star cluster. This study also found that some of the stars may not be red supergiants, but

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

stars.

References

{{DEFAULTSORT:Alicante 8 Asterisms (astronomy) Scutum (constellation) Scutum–Centaurus Arm