Stars well-endowed with gold have fewer companions

November 8, 2007

The chequered destinies of Australian Idol winners underscores what astronomers have known for a long time – star formation is complicated.

A new astronomical study adds an unexpected twist to the complications: stars well-endowed with gold and other heavy elements have fewer stellar companions. Researchers from The Australian National University (ANU) and the University of New South Wales (UNSW) believe their discovery could help track down Earth-like planets outside of our solar system.

“Ten years ago researchers found that stars with a large amount of heavy elements were more likely to be orbited by planets,” said report co-author Dr Charley Lineweaver from the Planetary Science Institute at ANU. “We still don’t understand why, but that’s the way it is. Our goal was to find out if such high-metallicity stars might also be more likely to be orbited by other stars.”

The Sun is a typical star in that about one per cent of its mass is made of heavy elements like oxygen, iron and gold. However, there are many stars with as little as one third of a per cent of their mass in heavy elements, while other stars have tens times that much. The amount of heavy elements somehow plays an important role in the types of object that form around a star.

Dr Lineweaver and Dr Daniel Grether from UNSW put together the most complete census of nearby stars, including the amount of heavy elements in these stars and whether the stars had planetary or stellar companions. They were surprised when they found the opposite of what was expected – stars with the highest content of heavy elements were less likely, not more likely, to have stellar companions.

“Our counterintuitive result does not yet have a good theoretical explanation, but we think that stars that form in different regions of our galaxy probably followed different paths to stardom,” Dr Grether said.

Detecting Earth-like planets has become a hot field for astronomers. Dr Lineweaver and Dr Grether believe that further research on the relationship between the amount of heavy elements in stars and the types of stellar and planetary companions orbiting them could assist in the search for worlds like our own.

The study is published in the latest edition of the Astrophysical Journal:
arxiv.org/abs/astro-ph/0612172

Source: Australian National University

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