Astronomers trace genealogic tree of the Milky Way
A team of international astronomers has shown how mapping the chemical composition of stars can help unravel the history of the Milky Way. Very little is known about the evolutionary process of the Milky Way, the galaxy in which our solar system is located. What we do know is that it started out just after the Big Bang as one or more diffused blobs of gas of almost pure hydrogen and helium. With time, it assembled into the flattened spiral galaxy, and generation after generation of stars were formed, including our Sun, some 4,700 million years ago. Now astronomers working at the European Southern Observatory (ESO) believe that they have uncovered an effective way to accurately date the stars and star clusters of the galaxy. They used the Ultraviolet and Visual Echelle Spectrograph (UVES) on ESO's Very Large Telescope to observe a dozen red giant stars found in Collinder 261, one of the oldest known open star clusters. 'Galactic star clusters are witnesses of the formation history of the Galactic disc,' says Kenneth Freeman, one of the members of the international team. 'The analysis of their composition is like studying ancient fossils. We are chasing pieces of galactic DNA!' From these observations, the astronomers were able to determine the chemical elements found in each star. They found that all stars in the cluster shared the same chemical signature. 'This high level of homogeneity indicates that the chemical information survived through several billion years,' explains Gayandhi De Silva, who led the research. 'Thus all the stars in the cluster can be associated to the same prehistoric cloud. This corroborates what we had found for two other groups of stars.' To further confirm their findings, the astronomers will now measure the chemical make-up of a larger sample of open clusters. By determining the 'DNA' of each star cluster, they believe it will be possible to trace the genealogic tree of the Milky Way. 'The path to an extensive use of chemical tagging is still long,' cautions Dr De Silva, 'but our study shows that it is possible. When the technique is tested and proven we will be able to get a detailed picture of the way our Galactic cradle formed.'