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RSAA News of the Month: November 2002

A Stellar Relic from the Early Milky Way
Have Astronomers Discovered the Oldest Star?

 

Astronomers have found a star that may have been one of the very first to form in our Milky Way galaxy. The star, HE0107-5240, is 80% as massive as the Sun, but has practically no metals in it, less than 1/200,000th the amount found in the Sun. This makes it the most metal-weak star ever found, an indication of extreme age. Younger stars have more metals* in their makeup because they form in regions that have been enriched by the chemicals produced by earlier generations of stars.

The critical observations were made by ANU Prof Mike Bessell, using the 2.3m telescope at Siding Spring. The star is one of thousands selected by his collaborator Dr Norbert Christlieb from the Hamburg/ESO Survey of metal weak stars. Bessell analyses the light emitted by the stars (their spectrum) and looks for the spectral features produced by Calcium atoms. HE0107-5240 had the weakest calcium lines that he had ever seen.

Dr Christlieb then used the most world's powerful high dispersion spectrograph on the Very Large Telescope at the European Southern Observatory in Chile to check out this remarkable star. "WOOOWWWW!!!" emailed Christlieb to their collaborators as soon as he looked at the spectrum. "The new star could be more than 10 times weaker in metals than anything we know of. This is the closest we have come to seeing the conditions directly after the Big Bang by studying stars."

According to current theories of star formation, low-mass metal-poor stars should not have formed at all. The theories obviously need to be improved. This raises the possibility that there may still be stars even poorer in metals, consisting only of material formed in the Big Bang. They would be an invaluable sample of the original chemistry of the Universe. Such a star may be well be found during the continuing survey by Bessell and Christlieb.

The original research is reported in the Oct 31, 2002 issue of the science journal "Nature" . To read the article, click here.

* Astronomers refer to all of the chemical elements other than hydrogen and helium as "metals".

Prof Mike Bessell (in dark trousers) and Dr Norbert Christlieb at the 2.3m telescope at Siding Spring Observatory

For more detail, click here.
To read the ESO press release, click here.
For a finding chart of HE0107-5240, click here.

For previous "RSAA News of the Month", click here.

© RSAA Nov 2002