Measuring stellar masses with asteroseismology

The team has performed a unique cosmic test—measuring the mass of an ancient star using two entirely different methods, and finding agreement to within just 1.4%. This result marks a milestone in our ability to determine the ages of old stars and use them as living fossils to study the Milky Way’s distant past.

They analyzed the red giant in the binary system KIC 10001167 using two independent approaches: 1) by exploiting the orbital motion, both in terms of eclipses and radial velocity as measured with respect to the observer, and 2) by modeling the internal oscillations of the red giant. The result? The seismic and orbital masses agree to within 1.4%, enabling a stellar age determination with an accuracy of about 10%.

The article "Advancing the accuracy in age determinations of old-disk stars using an oscillating red giant in an eclipsing binary" is published in Astronomy and Astrophysics Thomsen et al. 2025, A&A .

See also A&A news item with link to Bologna press release.

Illustration of the eclipsing binary system KIC10001167 with an up-close view of the orbit from our perspective (bottom left) and as seen from above (top right). The curves demonstrate what we can observe from earth, the amount of light coming from the system (top left) as well as the velocity of the two stars towards/away from us (bottom right). Credit: Jeppe Sinbæk Thomsen.

Crucially, this is the first time that such a high-quality seismic age estimate has been rigorously tested against an independent method — orbital dynamics — at a level of precision sufficient to verify the seismic method’s accuracy. Binary orbital motion is powerful as a tool to measure and validate the mass of stars determined with other methods, since it is well-described with the classical theory of gravity, which was established already in the 17th century by the works of Johannes Kepler and Isaac Newton.

“This is the first time we’ve been able to say, that a mass measured from an old star’s sound waves agrees within around one percent with a mass weighed from its orbit,” said Jeppe Sinkbæk Thomsen. The implications go beyond a single star. Because a star’s mass is the key to determining its age, this result validates the use of asteroseismology to accurately age-date old stars across the Galaxy. That, in turn, provides a powerful tool for reconstructing how the Milky Way assembled over billions of years.

This achievement anchors asteroseismology on firm empirical footing, especially at the old end of the age scale where independent benchmarks have been sorely lacking.

The result is based on observations with FIES at the NOT, and with participation from NOT staff and students in obtaining the data.

See also the IAC press release and Aarhus University press release .