An innovative new star map unites open clusters—previously studied in isolation—to compare and contrast stellar behavior across the Milky Way, scaling up the study of variable stars and providing astronomers with valuable new tools.
Such open clusters form what can be likened to natural laboratories for astronomers, since all of their stars were born out of the same material and are gravitationally bound. Given their similarities, they allow researchers a better opportunity to study the effects of variables such as mass and age on star behavior.
An Expanded View of the Cosmos
At the center of the new work are “variable stars,” named for their fluctuating brilliance. By studying observable changes in these stars’ brightness, researchers can gain insight into their internal physics. Traditionally, clusters and variable stars were analyzed independently, usually one at a time—a practice that left significant gaps in astronomers’ understanding of stellar behavior. To address this, Richard I. Anderson, head of the Standard Candles and Distances Laboratory at EPFL, and Emily Hunt of the Max Planck Institute for Astronomy, developed an unprecedented new star map.
The pair used data collected by the European Space Agency’s Gaia mission, cataloging almost 35,000 variable stars spread across 1,200 open clusters. Their map provides a foundation for researchers studying how stars are born, evolve, and eventually die—both in the context of their local communities and in comparison with their stellar siblings across the galaxy.
“It is a scientific first in the way that large samples of star clusters and variable stars are analyzed together,” says Anderson. “This creates synergies because the two approaches provide complementary insights.”
Gaia Satellite Observations
The Gaia satellite’s instruments capture precise data on stars’ position, brightness, and color. While the team focused on clusters within 6,500 light-years to ensure high-quality observations, Gaia has collected data on more than a billion stars in total.
The researchers combined cluster and variable star data to explore their relationships. First, they matched known variable stars to clusters, then examined each star’s brightness, distance, and age. By conducting this analysis on a large scale, the team identified trends in variable star behavior as clusters age, offering new context for stellar life cycles.
Although Gaia was turned off on March 27, the mission continues to excite scientists. Over the next few years, astronomers will process and analyze data on nearly 2 billion stars archived by the satellite.
“Our work is a teaser for what is to come with Gaia [data releases 4 and 5], which will revolutionize the study of stellar populations by their light variations,” says Anderson.
A Meaningful Star Map
The team found that variable stars are quite common, with brightness fluctuations over time occurring in about one-fifth of cluster stars. Variability is higher in younger clusters, while older clusters tend to display slower cycles similar to the Sun’s. One major breakthrough in their research was determining that certain types of variable stars serve as markers for an entire cluster’s age, providing astronomers with a much simpler way to estimate a cluster’s age without relying on complex modeling.
The researchers’ star catalog is now publicly available, containing the positions and properties of 35,000 variable stars. They also prepared a diagram showing how different types of variable stars are distributed across the Hertzsprung–Russell diagram, a common tool for tracking stellar evolution.
By exploring how these variable stars relate to their local clusters, the team has opened a valuable new avenue for studying the universe.
“We are made of stardust,” says Anderson. “Understanding the lives of stars and the physics that govern stars is crucial to understanding our origins and place in the cosmos.”
The paper, “A Bird’s-eye View of Stellar Evolution through Populations of Variable Stars in Galactic Open Clusters,” appeared in Astronomy and Astrophysics on August 13, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.