The RBC EXT8 globular cluster orbits the borders of the Andromeda Galaxy, a close buddy to our Milky Way Galaxy, situated 2.5 million light-years from Earth. Credit: ESASky/CFHT
Low-Metallicity Globular Star Cluster Challenges Formation Models
On the borders of the close-by Andromeda Galaxy, scientists have actually all of a sudden found a globular cluster (GC) — an enormous churchgoers of relic stars — with an extremely low abundance of chemical components much heavier than hydrogen and helium (called its metallicity), according to a brand-new research study.
The GC, designated RBC EXT8, has 800 times lower abundance of these components than the Sun, listed below a previously-observed limitation, challenging the concept that huge GCs might not have actually formed at such low metallicities.
GCs are thick, gravitationally bound collections of thousands to countless ancient stars that orbit in the fringes of big galaxies; lots of GCs formed early in the history of the Universe. Because they consist of a few of the earliest stars in a galaxy, GCs offer astronomers with a record of early galaxy development and development.
The most metal-poor GCs have abundances about 300 times lower than the Sun and no GCs with metallicities listed below that worth were formerly understood. This was believed to suggest a limitation to metal material — a metallicity flooring — that was needed for GC development; a number of systems have actually been proposed to discuss this limitation.
Søren Larsen and coworkers report the discovery of a very metal-deficient GC in the Andromeda Galaxy. Spectral analysis of RBC EXT8 reveals that its metallicity is almost 3 times lower than the most metal-poor clusters formerly understood, challenging the requirement for a metallicity flooring.
“Our finding shows that massive globular clusters could form in the early Universe out of gas that had only received a small ‘sprinkling’ of elements other than hydrogen and helium. This is surprising because this kind of pristine gas was thought to be associated with proto-galactic building blocks too small to form such massive star clusters,” stated Larsen.
Read Anemic Star Cluster Breaks Metal-Poor Record for more on this discovery.
Reference: “An extremely metal-deficient globular cluster in the Andromeda Galaxy” by Søren S. Larsen, Aaron J. Romanowsky, Jean P. Brodie and Asher Wasserman, 20 November 2020, Science.
DOI: 10.1126/science.abb1970
