An extraordinary cluster of massive stars near the centre of the Milky Way

Abstract

The relative numbers of newborn stars of different masses in a galaxy (the initial mass function) determines whether the galaxy's interstellar gas goes mainly into long-lived low-mass stars, as in the disks of normal spiral galaxies, or into short-lived massive stars, as has been proposed for "starburst" galaxies. The centre of the Milky Way is not a fully-fledged starburst region, but its star formation rate per unit volume of space is nevertheless roughly a thousand times that of the disk. It is, however, very difficult to study the initial mass function near the centre, because the dust in the gas clouds obscures the starlight, and the relatively rare young stars are mixed with much more numerous older stars. Here we report high-resolution infrared observations of a compact cluster of stars in the central region of our Galaxy. We find approximately 100 young, massive main-sequence stars, several of which seem to be among the most massive in the Galaxy. This cluster may be a weak analogue of the large star clusters in starburst galaxies, which opens the possibility of studying the starburst phenomenon through a local example.