Dr Claudia Reyes, the study's lead author and a PhD graduate from UNSW's School of Physics, analyzed the M67 cluster-a stellar family formed from the same gaseous cloud around four billion years ago. Despite sharing a common age and chemical makeup, these stars differ in mass, making them ideal models for studying stellar evolution.

"When we study stars in a cluster, we can see their whole sequence of individual evolution," Dr Reyes explained. Their varying masses determine their rates of evolution, and M67's diversity, including subgiants and red giants, provides a unique laboratory for this analysis.

This cluster is particularly valuable because it mirrors the conditions in which our Sun was born, offering potential clues about both the Sun's formation and its eventual transformation.

Professor Dennis Stello, a coauthor from UNSW Physics, emphasized the novelty of the approach. "This is the first time we have really studied such a long range of evolutionary sequences, like we have in this cluster," he said. Determining a star's age is notoriously difficult, as age indicators lie beneath the surface.

Because stars in M67 closely resemble the Sun in age and composition, they serve as analogues for studying the solar system's development and eventual fate. "Almost all stars are initially formed in clusters," Prof. Stello noted, describing them as stellar families born from massive gas clouds that typically disperse over time. Some clusters, however, remain gravitationally bound and visible in the night sky.

The study leveraged a technique called asteroseismology, using data from NASA's Kepler K2 mission to measure stellar oscillations. Each star 'rings' with a complex set of frequencies, determined by its internal structure, density, and temperature. These vibrations offer precise insights into a star's mass and age.

"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."

Large stars resonate at deeper frequencies, while smaller ones emit higher-pitched vibrations. No star produces just one tone; instead, they generate a spectrum of frequencies. Though sound can't travel in the vacuum of space, scientists detect these stellar vibrations as brightness variations.

As stars age and expand into red giants, their oscillation patterns shift. These changes reveal information about their internal layers and evolutionary stages. By comparing the large and small frequency separations within M67 stars, researchers can now apply the findings to characterize individual stars elsewhere in the galaxy.

Dr Reyes believes the study represents a breakthrough in mapping stellar ages and masses across the Milky Way. Such data are critical to understanding how galaxies form and evolve, and also impact how we assess the habitability of planets around other stars.

Prof. Stello highlighted that the study refines stellar evolution models, particularly for solar-type stars. "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," he said.

Research Report:Dr Reyes added that the discovery of distinct frequency patterns was unanticipated. "We discovered something new with this signature in the frequencies," she said. The next step, she suggested, is to reexamine existing galactic data to search for similar patterns that may have previously gone unnoticed.

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University of New South Wales
Stellar Chemistry, The Universe And All Within It