A sprinkling of distant star clusters.

A sprinkling of distant star clusters

Our own galaxy has about 150 satellites, each one a compact cluster containing a million or so stars. How and when these "globular clusters" formed is still something of a puzzle, and astronomers have been looking for clues by examining globular clusters surrounding nearby galaxies. Two astronomers have now detected a population of globular clusters around a remote galaxy known as NGC 6166. This particular "supergiant" galaxy, about 400 million light-years from Earth, lies at the center of a large group of galaxies called Abell 2199.

"This is the most distant galaxy in which globular clusters have been found," says William E. Harris of McMaster University in Hamilton, Ontario. Harris and C.J. Pritchet of the University of Victoria in British Columbia detected faint, starlike objects in the NGC 6166 vicinity with exactly the characteristics expected of bright globular clusters at the outskirts of a galaxy.

Unlike other supergiant, elliptical galaxies, which may have 15,000 or more globular clusters, NGC 6166 has a more modest complement of satellites. Harris and Prichet suspect this particular galaxy may be the result of an extended series of mergers with other galaxies in a relatively congested region of the universe. Such mergers would swallow up a significant proportion of any globular clusters present, gradually reducing the cluster population to a level below that expected for a galaxy of this size. The astronomers say this scenario supports the argument that globular clusters, which typical contain old stars, have existed from the very start of the period of galaxy formation. It strongly argues the idea that globular clusters surrounding giant galaxies form continuously as a result of the condensation of high-temperature gas flowing from a galaxy's fringes toward its center