News in Science

Mysterious star challenges view of clusters

Mystery star Mystery surrounds the discovery of a very young star deep in the midst of an ancient stellar cluster.

If the star is as young as it seems, the finding, published this week in the journal Astronomy and Astrophysics, challenges our current understanding of the nature of such clusters.

The Milky Way galaxy is orbited by more than 150 globular clusters, which are tight balls of tens of thousands of ancient stars dating back to the distant past of the universe.

There has been a long-standing belief that all stars in globular clusters are born at the same time, whereas stars in galaxies can be of different ages.

But astronomers using the European Southern Observatory's La Silla telescope in Chile have now made a discovery that undermines this idea.

While studying what's known as a globular cluster, called Messier 4, 7200 light years away, in the constellation Scorpius, they found a star that is much younger than those around it.

"[The] star #37934, shows remarkably high lithium abundance, compatible with current estimates of the primordial lithium abundance," researchers report.

Lithium is normally gradually destroyed over a star's life. But this one star among thousands, has somehow either managed to retain its original lithium, or found a way to enrich itself with freshly made lithium from other stars.

The star was discovered in spectroscopic observations used to study the chemical composition and age.

"The evidence suggests that the high lithium abundance of star #37934 may originate by pollution from a previous generation of stars," the researchers write.

They say the recent detection of a lithium-rich star of pollution origin in another globular cluster may also point in this direction.

However they say there's not enough evidence to rule out the possibility that star #37934 has somehow kept its primordial lithium abundance.

A lot to learn

Astronomy Professor Duncan Forbes from Melbourne's Swinburne University says this discovery shows how much scientists still need to learn about something they thought was very simple and well understood.

"This further blurs the distinction between globular clusters and galaxies," says Forbes.

"We used to think all the stars in a globular cluster formed at the same time from the one molecular gas cloud, so they all have the same chemical composition ... We now know that's clearly not the case," he adds.

"So maybe we need another classification scheme that unites more massive globular clusters and galaxies."