Indian astronomers have uncovered a hidden structure in the Milky Way after discovering that a group of stars previously classified as a single star cluster is actually made up of two distinct stellar systems. The discovery provides a rare opportunity to study how star clusters interact gravitationally and evolve after passing close to one another.
The system, known as UBC 63, is located approximately 4,892 light-years from Earth. It was earlier identified as a single, relatively sparsely populated open star cluster. However, a detailed investigation using astronomical observations and advanced computer modelling has revealed two separate populations, now designated UBC 63A and UBC 63B.
Editorial Insight
Key Highlights
Important points readers should notice.
Issue/Event: Indian astronomers identify two separate star clusters hidden within the previously classified UBC 63 system.
Location: India.
Authority/Organisation: Gauhati University, Indian Institute of Astrophysics and Department of Science and Technology, with international research collaborators.
Action Taken: Researchers analysed ESA Gaia observations, stellar movements and computer simulations to identify and reconstruct the two clusters' close encounter.
Impact: The findings offer new insights into gravitational interactions, stellar populations and the evolution of star clusters in the Milky Way.
The research was led by astronomers from India, including researchers associated with Gauhati University and the Indian Institute of Astrophysics (IIA), an autonomous institution under the Department of Science and Technology. The team used data from the European Space Agency's Gaia mission to investigate the positions, movements, brightness and colours of stars within the system.
The researchers noticed two distinct sequences in the colour-magnitude diagram, an important astronomical tool used to understand the properties and evolutionary stages of stars. This provided evidence that UBC 63 might contain two different stellar populations rather than one unified cluster.
Further analysis of stellar movements, machine-learning techniques and high-performance computer simulations confirmed the presence of two distinct clusters.
Editorial Analysis
Why This Matters
The discovery is important because star clusters help astronomers understand how galaxies develop and how gravitational forces shape groups of stars over millions of years. Identifying two distinct systems within what was previously considered one cluster allows scientists to study their separate origins, different ages and past interaction. The findings also highlight the growing importance of combining large-scale astronomical observations with machine learning and advanced simulations. Such approaches can help researchers identify structures that conventional observations may overlook. For India's scientific community, the research demonstrates the international contribution of Indian astronomers to advanced space science and astrophysics.
Two clusters with very different ages
One of the most significant findings concerns the age difference between the two stellar systems.
UBC 63A is estimated to be approximately 21 million years old, making it the younger cluster. UBC 63B, meanwhile, is estimated to be around 562 million years old.
The substantial difference in their ages indicates that the two systems did not originate together as one star cluster. Instead, they developed independently and later came close to each other during their movement through the Milky Way.
A close encounter millions of years ago
The researchers reconstructed the movement of both clusters through the galaxy using orbital calculations and dynamical simulations.
Their analysis suggests that the two systems came remarkably close to one another approximately six million years ago. At their closest estimated approach, the separation was around seven parsecs, equivalent to approximately 23 light-years.
At the time the younger cluster formed, the two systems were separated by about 60 parsecs, or roughly 196 light-years.
Today, they are approximately 26 parsecs apart, equivalent to about 85 light-years. Their relative motion indicates that they are not gravitationally bound to each other and are moving apart following their close encounter.
The research therefore offers scientists an opportunity to investigate the effects of a relatively recent stellar flyby without assuming that the two clusters merged or became a single gravitationally connected system.
Why the discovery matters
Star clusters are important building blocks of galaxies. Their structure and movement can provide clues about how stars form, how gravitational interactions influence stellar populations and how galaxies evolve over long periods.
The discovery of two clusters with significantly different ages in such close proximity provides an unusual natural laboratory for studying these processes.
It also demonstrates the scientific value of the Gaia space mission, which measures the positions and movements of stars with exceptional precision. Such measurements can reveal hidden structures that may not be apparent when astronomers examine only the apparent positions of stars in the sky.
The research has been published in The Astronomical Journal. The findings strengthen the contribution of Indian researchers to modern astronomy and the study of stellar evolution.
