The Arches star cluster lives near the black hole in the centre of our galaxy, and contains around 1,000 stars.
Star family lives in a crowded, violent place
6 Jun 2009
Astronomers have obtained one of the sharpest views ever of the Arches Cluster—an extraordinarily dense group of young stars that lives near the huge black hole at the heart of our Milky Way galaxy.
Despite the extreme conditions, the astronomers were surprised to find the same proportions of low- and high-mass young stars in the cluster as are found in more tranquil locations in the Milky Way.
The massive Arches Cluster is a rather peculiar star cluster. It is located 25,000 light-years away towards the constellation of Sagittarius (the Archer), and contains about a thousand massive stars, each less than 2.5 million years old—which is very young by astronomical standards.
The Arches is an ideal "laboratory" for studying how massive stars are born in extreme conditions. Being so close to the centre of our Milky Way, it experiences huge opposing forces from the stars, gas and the black hole that reside there.
The cluster is ten times heavier than typical young star clusters scattered throughout our Milky Way, and is enriched with chemical elements heavier than helium.
Studying the Arches Cluster is very challenging because of the huge quantities of absorbing dust between Earth and the Galactic Centre, which visible light cannot penetrate. So the astronomers analysed the region by picking up near-infrared light wavelengths.
The new study confirms the Arches Cluster to be the densest cluster of massive young stars known. It is about three light-years across, with more than a thousand stars packed into each cubic light-year—this is a million times greater than the density of stars in the Sun's neighbourhood.
And some of the cluster's stars are big.
"The most massive star we found has a mass of about 120 times that of the Sun," says astronomer Fernando Selman.
The name "Arches" does not come from the constellation the cluster is located in (Sagittarius, ie. the Archer), but because it is located next to arch-shaped filaments of gas seen in radio wavelength maps of the centre of the Milky Way.
Adapted from information issued by ESO.
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