"We still don't understand how the more than 100 billion galaxies in our universe formed and evolved. Now we are going back to the very beginning of the Milky Way and using the astronomical equivalent of fossils to understand how our galaxy and those beyond it came about," said Gayandhi De Silva, from the University of Sydney's School of Physics, according to a press release.
"Until now if we wanted to understand how the beautiful star clusters inside the Milky Way formed, or the spectacular spiral galaxies beyond it, we were limited to studying, at the very most, a few hundred stars from near the Sun," De Silva continued. "By contrast GALAH probes ten times further into the galaxy and is the first attempt to survey a million stars to create a dataset that will be used by astronomers worldwide for decades to come."
The GALAH survey is an international five-year project, led by Australia, involving 70 astronomers from 17 institutions in eight countries.
The survey is led by De Silva and Joss Bland-Hawthorn from the University of Sydney, as well as Ken Freeman from the Australian National University.
"Galactic archaeology means we 'dig down' into the chemical origin of stars to find out where they came from and how they formed," said Bland-Hawthorn, according to the press release. "Stars formed very early in our galaxy only have a small amount of heavy elements such as iron, titanium and nickel. Stars formed more recently have a greater proportion because they have recycled elements from other stars."
"We reach back to capture this chemical state -- by analyzing the mixture of gases from which the star formed," Bland-Hawthorn continued. "You could think of it as its chemical fingerprint -- or a type of stellar DNA from which we can unravel the construction of the Milky Way and other galaxies."
The Milky Way is constantly in motion, and stars that were born during its formation may have moved all the way to its other end - well away from their birth sites. Also, not all the stars that call the Milky Way home were born there -- they may have been forcibly pushed into it from outside galaxies as the gravitational pull of the Milky Way cannibalizes its satellites.
The scientists will use HERMES to measure up to 29 chemicals in the stars, as well as the stars' temperature, gravity and velocity to inform their understanding.
"Instead of only relying on what we can discover from their current positions GALAH allows us to trace the stars' origins -- including the origin of our Sun -- and map their growth and movement through time and space," De Silva said, according to the press release. "Our archaeology of space is a new era in astronomy and the knowledge gained promises to be every bit as exciting and important as anything discovered on Earth."
Reference:
"The GALAH Survey: Scientific Motivation," G. M. De Silva et al., Monthly Notices of the Royal Astronomical Society, 2015 [https://mnras.oxfordjournals.org/content/449/3/2604.full, preprint: https://arxiv.org/abs/1502.04767].
Additional authors from the University of Sydney on the Royal Astronomical Society paper are: Sanjib Sharma, Geraint Lewis and Dennis Stello. Other contributing authors are from the Australian Astronomical Observatory, Australian National University, University of NSW, Macquarie University, University of Ljubljana, University of Southern Queensland, the Max-Planck Institute, Monash University, University of Cambridge, Astronomical Observatory of Padova, Michigan State University, University of Minnesota, University of Western Australia, Uppsala University and the Harvard-Smithsonian Center for Astrophysics.
