14 DAY TRIAL // Galaxies and their origin and evolution are a major interest area for astronomers, and in particular of our host galaxy, the Milky Way.
Since a detailed physical scenario of its birth and growth is still missing, its understanding requires the joint effort of observations, theories and complex numerical simulations.
ESO astronomer Gayandhi De Silva and her colleagues used the Ultraviolet and Visual Echelle Spectrograph (UVES) on ESO's Very Large Telescope to find new ways to address this fundamental riddle.
They have shown how to use the chemical composition of star clusters to shed light on the formation of our galaxy, and this discovery will be a fundamental test for the development of a new chemical tagging technique.
"We have analyzed in great detail the chemical composition of stars in Three star-clusters and shown each cluster presents a high level of homogeneity and a very distinctive chemical signature", says De Silva, who started this research while working at the Mount Stromlo Observatory, Australia. "This paves the way to chemically tagging stars in our Galaxy to common formation sites and thus unraveling the history of the Milky Way", she adds.
Open star clusters are among the most important tools for the study of stellar and galactic evolution.
They are composed of a few tens up to a few thousands of stars that are gravitationally bound, and they span a wide range of ages.
The youngest date from a few million years ago, like The Pleiades, a young bright cluster, while the oldest and more rare can have ages up to ten billion years, like Collinder 261, located about 25 000 light years from the Galactic Center, which was the target of the present team of astronomers, and can provide useful information on the early days in the existence of our galaxy.
Using UVES, they observed a dozen of red giants in the open cluster Collinder 261, since they are more luminous, thus well suited for high-precision measurements.
From these observations, the abundance of a large set of chemical elements could be determined for each star, clearly demonstrating that all the stars in the cluster share the same chemical signature. "Thus all the stars in the cluster can be associated to the same prehistoric cloud", explains De Silva, while another member of the team, Kenneth Freeman stated: "The analysis of their composition is like studying ancient fossils. We are chasing pieces of galactic DNA!"
Once the "DNA" of each star cluster is inferred through this chemical mapping, it will someday be possible to trace the genealogical tree of the Milky Way, even though the path to an extensive use of chemical tagging on galaxies is still long.