Astronomers tune into the music of a nearby star to unlock a surprising discovery

Astronomers using W. M. Keck Observatory on Maunakea, Hawaiʻi Island have listened to the music of a nearby star, uncovering surprises that shake our understanding of how stars work.

The study used Keck Observatory’s latest cutting-edge instrument, the Keck Planet Finder (KPF), to detect oscillations rippling through a star. The findings, published today in the The Astrophysical Journal, open a new window into the interiors of stars that were once thought too quiet to probe.

A stellar symphony

Although we cannot directly hear them with our own ears, stars are not silent. Like musical instruments, stars resonate with natural frequencies that astronomers can “hear” with the right tools. This field of research—known as asteroseismology—allows scientists to use these frequencies to probe the interiors of stars, just as earthquakes help scientists learn about Earth’s interior.

“The vibrations of a star are like its unique song,” said Yaguang Li, lead author and researcher at the University of Hawaiʻi at Mānoa. “By listening to those oscillations, we can precisely determine how massive a star is, how large it is, and how old it is.”

Until now, “stellar songs” had mostly been recorded from stars hotter than the sun, using NASA space telescopes like Kepler and TESS. But the oscillations of HD 219134—a cooler, orange-colored star just 21 light-years away—are too subtle to pick up using brightness variations that are probed by space-based telescopes.

Keck Observatory’s KPF instrument precisely measures the motion of the stellar surface toward and away from the observer. Over four consecutive nights, the team used KPF to collect over 2,000 ultra-precise velocity measurements of the star—enabling them to catch the star’s vibrations in action. This is the first asteroseismic inference of the age and radius for a cool star using KPF.

“KPF’s fast readout mode makes it perfectly suited for detecting oscillations in cool stars,” added Li, “and it is the only spectrograph on Mauna Kea currently capable of making this type of discovery.”

A 10-billion-year-old time capsule

Using the oscillations detected in HD 219134, the team determined its age to be 10.2 billion years, more than twice the age of our sun. This makes it one of the oldest main-sequence stars with an age determined using asteroseismology.

This measurement is more than just a curiosity—it has major implications for how we understand stellar aging. Astronomers use a method called gyrochronology to estimate stellar ages based on how quickly they spin. Young stars rotate rapidly, but they gradually slow down as they lose angular momentum over time—much like spinning tops that wind down.

But something curious happens with stars like HD 219134: their spin-down seems to stall at older ages. The new asteroseismic age allows scientists to anchor models at the old end of the stellar timeline, helping to refine how we estimate the ages of countless other stars.

“This is like finding a long-lost tuning fork for stellar clocks,” said Dr. Yaguang Li. “It gives us a reference point to calibrate how stars spin down over billions of years.”

A puzzle in the star’s size

Surprisingly, the team also discovered that HD 219134 appears smaller than expected. While other measurements using interferometry—a technique that measures a star’s size by observing it with multiple telescopes—gave a radius about 4% larger, the asteroseismic measurement suggests a more compact star.

This difference is puzzling and challenges assumptions in stellar modeling—especially for cooler stars like HD 219134. Whether the discrepancy is due to unrecognized atmospheric effects, magnetic fields, or deeper modeling issues remains an open question.

The star HD 219134 is not alone—it hosts a family of at least five planets, including two rocky, super-Earth-sized worlds that transit across the star’s face. With a more precise measurement of the star’s size, the team was able to refine the sizes and densities of these planets. Their updated values confirm that these worlds likely have Earth-like compositions, with solid, rocky surfaces.

Stellar sounds and the search for life

Instruments like the Keck Planet Finder will enable measurements for other stars like HD 219134, which will become the focus for searching for life on other planets in the coming decades using future NASA Missions such as the Habitable Worlds Observatory.

“When we find life on another planet, we will want to know how old that life is.” said Dr. Daniel Huber, a co-author on the study. “Listening to the sounds of its star will tell us the answer.”