Astronomers collect spectra in search for Sun’s lost siblings

Australian astronomers are collecting the spectra of a million stars across the Milky Way to learn more about galactic evolution. In the process, they hope to track down at least some of the Sun’s lost siblings. Image: Roanish, Flickr

Australian astronomers have collected spectra from more than 340,000 stars across the Milky Way in a project aimed at building a database that will shed light on the galaxy’s formation and evolution and allow researchers to track down stars born in the Sun’s birth cluster that have long since scattered.

The custom-built HERMES spectrograph, attached to the Australian Astronomical Observatory’s 3.9-metre Anglo-Australian Telescope, collected the spectra over more than 280 nights as part of the Galactic Archaeology project, known as GALAH. The project’s first major data release was announced 18 April.

“No other survey has been able to measure as many elements for as many stars,” Gayandhi De Silva of the University of Sydney, the HERMES instrument scientist, said in a release.

“This data will enable such discoveries as the original star clusters of the galaxy, including the Sun’s birth cluster and solar siblings. There is no other dataset like this ever collected anywhere else in the world.”

The Sun was born nearly five billion years ago in a cluster likely containing several thousand stars. Since then, the original birth cluster has dissipated, but using software developed for the GALAH project astronomers should be able to compare spectra, identifying stars with similar compositions and history.

“Every star in that cluster will have the same chemical composition, or DNA,” said Sarah Martell of the University of New South Wales in Sydney, leader of the GALAH survey observations. “These clusters are quickly pulled apart by our Milky Way Galaxy and are now scattered across the sky. The GALAH team’s aim is to make DNA matches between stars to find their long-lost sisters and brothers.”

The computer code used for the data analysis is known as “The Cannon,” after American astronomer Annie Jump Cannon, who spent several decades visually classifying the spectra of about 340,000 stars a century ago.

“We train The Cannon to recognise patterns in the spectra of a subset of stars that we have analysed very carefully, and then use The Cannon’s machine learning algorithms to determine the amount of each element for all of the 340,000 stars,” said Sven Buder, a Ph.D. student at the Max Planck Institute for Astronomy in Germany.

The GALAH data release was timed to coincide with the release of data from the European Space Agency’s Gaia satellite on 25 April. Gaia has mapped the positions of more than 1.6 billion stars across the Milky Way. The GALAH survey, which eventually will collect spectra from about a million stars, will add stellar velocities to the mix.

Says Sanjib Sharma from the University of Sydney: “For the first time, we’ll be able to get a detailed understanding of the history of the Galaxy.”