Two thousand seven hundred light years away from Earth, stars in a distant galaxy are “singing” in a chorus of cosmic proportions. Now, University of New South Wales, Sydney (UNSW) researchers are listening in on this stellar song with hopes of uncovering the mysteries of stellar evolution and mapping the history of galaxies.
Led by Dr Claudia Reyes, the project investigated the 27 stars of cluster M67, which were born from a gas cloud four billion years ago. In their research, the team made significant strides in measuring stars from across great distances, allowing scientists to study galaxies like never before.
Ideal Candidates
“When we study stars in a cluster, we can see their whole sequence of individual evolution,” Dr Reyes said.
M67 was an ideal focus for the team’s research due to the stars’ shared chemical makeup and varying masses. Although born simultaneously, the stars evolve at different speeds, a fact revealed by how much mass they’ve gained relative to one another. The cluster features a wide range of giant stars, from smaller subgiants to massive red giants. Studying M67 also provides valuable insights closer to home, as our Sun formed in a similar environment and is expected to follow a comparable evolutionary path.
“Almost all stars are initially formed in clusters,” said co-author Prof Dan Stello, also of UNSW. “They are basically big families of hundreds to thousands of stars born from one big cloud of gas.
“Usually, they would slowly disperse into a diffuse random selection of stars,” Stello added. “But some of them are still within groups – clusters. You can see them when you look to the sky as areas with lots of stars close together, where they are still closely bound, like the cluster we studied here.”
Listening to the Songs of Stars
Until now, scientists had never achieved such a detailed observation of stellar evolution within a single cluster. “This is the first time we have really studied such a long range of evolutionary sequences, like we have in this cluster,” Prof. Stello said.
The main challenge in observing stars lies in the fact that their surfaces don’t reveal their age—only their interiors hold that information.
Stellar giants emit unique frequencies based on their physical properties, such as density, temperature, and age. Dr. Reyes’s team “listened” to them using NASA’s Kepler K2 space telescope—the first time this has been done across an entire star cluster. Since there is no sound in space, the researchers extrapolated frequencies by monitoring how the stars alternated in brightness as they heated and cooled.
“The frequency by which an instrument is vibrating – or ringing – depends on the physical properties of the matter that the sound travels through,” Prof. Stello said. “Stars are the same. You can ‘hear’ a star based on how it rings.”
Like a conductor tuning into individual instruments in an orchestra, the team isolated stars from the larger chorus. By studying their oscillation frequencies, they determined the age and mass of each star. Larger stars produce lower, deeper tones, while smaller stars resonate at higher pitches—much like thick and thin guitar strings. And like musical chords, each star produces multiple frequencies at once.
Cosmic Vibrations
“We can see the vibration – or the effect of the vibration – of the sound just like you can see the vibration of a violin string,’ Prof Stello commented. “It’s these fluctuations in brightness that we watched and measured, to gauge the sound frequencies.”
The different nodes inside the stars play different notes, indicating their interior properties. Along their evolutionary journey, stars change frequencies, allowing outside observers to track stellar progress.
This is the first time scientists recorded the frequency differences between giant stars in a cluster, providing important contextual information for studying individual stars in the future.
The Next Phase of Cosmic Music
Building on this research, scientists can now more accurately measure the age and mass of stars in the Milky Way. That data, in turn, improves our understanding of galactic evolution—and may even assist in the search for extraterrestrial life, since stars are critical to sustaining life on surrounding planets.
“This study has enabled us to probe the fundamental physics that happens inside stars, deep into their interiors, and the fundamental physics under these extreme conditions,” Prof Stello said. “This is something we still grapple with. It’s important for us to build evolution models that we can trust, so that we can predict what happens not only to the Sun, but also to other stars as they grow older.”
“Seeing the evolutionary phase of stars directly through the fingerprint of frequencies is what enables us to be much more certain about the ‘ingredients’ we put into our models,” Prof Stello added.
“We discovered something new with this signature in the frequencies,” Dr Reyes concluded. “The next step is to go back and look at that data to look for these particular frequencies that nobody thought to look for before. And we can do this by listening to the stars.”
The paper “Acoustic Modes in M67 Cluster Stars Trace Deepening Convective Envelopes” appeared in Nature on April 2, 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.