Astronomers from the Australian National University (ANU) have made a world-first discovery of binary stars in a dense star cluster, which they believe could be the first step in building a more complete picture of how our galaxy formed.
The finding is part of the Legacy Survey of Space and Time (LSST), a decade-long project using the Vera C. Rubin Observatory in Chile to scan the entire southern sky every few nights, creating what ANU astronomer Dr Giacomo Cordoni called a “movie of the universe”.
“This survey … will allow us to track billions of stars and galaxies as they change over time. It’s designed to unravel the history of star clusters, galaxies and the Milky Way itself.”
The team focused on 47 Tucanae, one of the brightest globular clusters (ancient and crowded systems holding hundreds of thousands of stars tightly packed together, “making them natural laboratories to study how stars evolve and interact”).
47 Tucanae can be seen with the naked eye from the Southern Hemisphere and is often used as a benchmark for models of cluster evolution, Dr Cordoni explained.
For the first time, ANU astronomers detected binary stars (pairs of stars orbiting a common centre of gravity) in the outer regions of the cluster. Binary stars exchange energy with their neighbours, influence whether a cluster survives for billions of years, and can give rise to exotic objects such as luminous blue stars known as blue stragglers.
The ANU scientists found that binaries are three times more common in the outskirts than in the dense central regions (previously studied with the Hubble Space Telescope) — evidence that binaries are destroyed or disrupted in the crowded centre, but can survive in the quieter outskirts.
“This is remarkable because 47 Tucanae has been studied for over 100 years, but only now, thanks to Rubin, we can map its outskirts in detail and understand what’s really happening there, and how these mysterious clusters assembled,” study co-author Professor Luca Casagrande said.
“This discovery is a crucial new piece of the puzzle of how globular clusters — some of the Milky Way’s oldest inhabitants — formed and evolved.”
Co-author Professor Helmut Jerjen said the results show the transformative power of the Rubin Observatory.
“Even in its first test data, LSST is already opening a new window on stellar populations and dynamics. Over the coming decade, Rubin will map binaries and other stars across the entire sky, providing the first complete census of these systems and delivering a decisive test for theories of how clusters and galaxies came together to build the universe we see today.”
