Washington, May 31 : Researchers at the McMaster University in Hamilton, Ontario, have discovered unexpected populations in globular clusters, a finding that suggests life in the stellar nursery was not as simple as astronomers had previously thought.

"We thought we understood these clusters very well," said Dr. Alison Sills, Associate Professor of Physics and Astronomy.

"We taught our students that all the stars in these clusters were formed at the same time, from one giant cloud of gas. And since that time, the individual stars may have evolved and died, but no new stars were born in the cluster," she added.

In the middle of the last century, a population of stars called blue stragglers was discovered. These stars are hotter and brighter, and more massive, than they should be for a cluster of this advanced age.

The current explanations for these stars involve some kind of stellar interaction. Two normal stars get too close to each other, and the gravity of one can pull material off the surface of the other, causing the two stars to merge.

With the help of Hubble Space Telescope, Sills and her colleagues found evidence for two generations of star formation, not just one. But the second generation is not the same as anywhere else in the Galaxy.

Instead of being made of material that came from an earlier generation of exploded stars, the second generation in globular clusters seems to have come from material that was gently shed by the first generation of stars.

This link between the two generations is puzzling, and astronomers are still trying to figure out why globular clusters should behave in this way.

"Studying the normal stars in clusters was instrumental in allowing astronomers to figure out how stars lived and died, "said Sills, "but now we can look even further back, to when they were born, by using the oddballs. It pays off to pay attention to the unusual individuals in any population. You never know what they''ll be able to tell you."

The findings will be presented at a meeting of the Canadian Astronomical Society in Ontario. (ANI)