A world-first glimpse into the outskirts of a globular cluster
A landmark discovery from the Australian National University (ANU) points to a new way of understanding how our galaxy formed. By tapping into the Rubin Observatory’s Legacy Survey of Space and Time (LSST), researchers detected binary stars—pairs that orbit a common center of gravity—in the outer regions of the globular cluster 47 Tucanae for the first time. This finding, made with Rubin’s first public data release, offers a fresh perspective on how these ancient stellar cocoons evolve and cling to life across billions of years.
What makes globular clusters and binary stars so important?
Globular clusters are among the oldest structures in the Milky Way, housing hundreds of thousands of stars packed into relatively compact volumes. They serve as natural laboratories for studying stellar evolution and the dynamic interactions that sculpt star systems over time. Within these clusters, binary stars play a pivotal role. By exchanging energy with neighboring stars, binaries influence whether a cluster endures for eons and can even birth exotic objects, such as luminous blue stars known as blue stragglers.
The Rubin Observatory’s transformative role
The discovery is part of an ambitious 10-year program to scan the entire southern sky with Rubin Observatory in Chile, tracking billions of stars and galaxies as they change over time. Led by ANU researcher Dr. Giacomo Cordoni, the project is designed to assemble a continuous “movie of the universe”—an unprecedented dynamical census of celestial populations. As Dr. Cordoni noted, this approach will unravel the history of star clusters, galaxies, and the Milky Way itself, offering a more complete picture of cosmic evolution.
First public data, first new insights
Using Rubin’s Data Preview 1, ANU astronomers mapped binary stars across the outskirts of 47 Tucanae, finding a striking contrast: the frequency of binaries there is roughly three times higher than in the cluster’s dense core, a region previously studied mainly with the Hubble Space Telescope. The contrast suggests a protective dynamic—binaries in sparser outer regions can endure disruptive encounters that are common in crowded centers. This reveals that the outskirts may preserve a closer approximation to the cluster’s original stellar population.
Why this matters for the history of star clusters
The results are a crucial piece of the puzzle in explaining how globular clusters formed and evolved. If outer regions retain a larger share of primordial binaries, models of cluster assembly must account for this spatially uneven survival. Such insights help calibrate theories about how the Milky Way’s oldest inhabitants came together and how interactions among stars shape long-term stability. In turn, this informs broader questions about galaxy formation and the distribution of stellar remnants across cosmic time.
A decade of discovery ahead
Researchers stress that Rubin’s ongoing survey will deliver a complete census of binary stars and other stellar populations across the sky, enabling decisive tests of existing theories about cluster and galaxy assembly. The collaboration’s early success demonstrates the Rubin Observatory’s power to transform our understanding of the universe, even in its initial data releases. Over the coming years, astronomers expect to map how binary stars and other systems evolve as the cosmos unfolds, offering new context for the Milky Way’s history and our place within it.
Looking forward
The ANU-led findings, soon to be published in PASA Letters, underscore a broader shift in astrophysics: with large-scale, time-domain surveys, scientists can watch celestial structures in motion. As Rubin continues to collect data, the “movie of the universe” will become increasingly detailed, enabling more discoveries about globular clusters, stellar dynamics, and the processes that shaped our galaxy’s past—and may determine its future.
