The synchronization of stellar clocks allows us to understand the formation of stars and their dispersion

Researchers from the University of Vienna and the Center for Astrobiology (CAB), INTA-CSIC, have discovered an age difference between two of the most reliable methods for measuring stellar age: isochronous and dynamical tracks, based on their movement through the galaxy.

According to their calculations, the age from dynamical tracks is systematically about 5.5 million years younger. This important finding suggests that the dynamical track’s ‘clock‘ starts counting when a stellar association begins to expand after leaving its parent cloud, while the isochronous ‘clock’ begins from the moment of initial star formation.

This information has relevant implications for our understanding of star formation and stellar evolution, including the formation of planets and the formation of galaxies. This allows existing models to be tested in order to offer a new perspective on the chronology of star formation. The article detailing these results was published in Nature Astronomy.

Stellar age is a fundamental parameter in astrophysics. However, it is one of the most difficult measurements to make. The best estimates correspond to star clusters, i.e. groups of stars of the same age with a common origin. Numerous techniques are used to estimate stellar ages, but they often produce contradictory results.

Scientists wondered whether the age differences between different techniques are due to uncertainties in models and observations or whether this age puzzle could be used to learn something about the process of star formation.

David Barrado, researcher at the National Institute of Aerospace Technology (INTA) at CAB, explains: “Determining the age of a cosmic process is a fundamental problem. This work lays very solid foundations to seek global solutions. The ESA PLATO space telescope, which will be launched at the end of 2026, will be the key to the complete solution.”

Núria Miret-Roig, for her part, first author of this study and researcher at the University of Vienna, points out: “Astronomers use isochronous ages based on our understanding of how stars work, and these ages depend on the specific model we use.”

The high-quality data from the Gaia satellite, she notes, “allow us to measure age dynamically, independently of stellar models, and we were thrilled to be able to synchronize the clocks; that is, testing the different models. We found a consistent and puzzling difference between the two dating methods.”

According to the scientist, they have reached a point where they can no longer blame the discrepancy on observational error; therefore, it was most likely that the two clocks “measured two different things.”

This age difference between the two methods “represents a new tool and a much-needed one for quantifying the earliest stages of the life of a star,” says João Alves, co-author and professor at the University of Vienna. “It allows us to measure how long it takes for baby stars to leave the nest,” he adds.

This information is essential for the further development of our understanding of the early life of stars and the evolution of star clusters.

The researchers analyzed six nearby (closer than 500 pc, based on the length unit parallax of an arcsecond) and young clusters (ages less than 50 million years). They showed that the timescale of the embedded phase is approximately 5.5 million years, with an uncertainty of only one million, and could depend on the cluster mass and the amount of stellar feedback.

Applying this new technique to other young clusters in the solar neighborhood, where observational accuracy is better, will provide new insights into the process of star formation and dispersion.

According to the authors, this work was possible thanks to the excellent astrometry of the Gaia space mission in combination with ground-based radial velocities (like those in the APOGEE catalog) that allow precise velocity measurements in three dimensions to trace the positions of the stars back in time to their birthplace.

New and future spectroscopic surveys such as WEAVE, 4MOST and SDSS-V will enable this study across the entire solar neighborhood.

In the words of Miret-Roig: “Our work paves the way for future research on star formation and provides a clearer picture of how stars and star clusters evolve. It is a significant step in our quest to understand the formation of the Milky Way and other galaxies.”