By studying faint vibrations within stars, scientists using the Keck Planet Finder have discovered internal features that call long-standing models into question.
Astronomers at the W. M. Keck Observatory on Maunakea, Hawaiʻi Island have detected unexpected signals from a nearby star, revealing insights that challenge current ideas about stellar behavior.
Using the Keck Planet Finder (KPF), the observatory’s most advanced instrument, the team measured oscillations within the star, subtle vibrations once thought undetectable. The results, published in The Astrophysical Journal, provide a new way to study the internal structure of stars previously considered too inactive to analyze.
A Stellar Symphony
Stars may seem silent to us, but they are constantly vibrating with natural frequencies that, while inaudible to human ears, can be detected with specialized instruments. Much like musical instruments, these celestial bodies produce resonant tones. Through a field called asteroseismology, scientists study these stellar vibrations to explore a star’s internal structure, much like how geologists use seismic waves to investigate the inside of Earth.
“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.”
Artist’s concept of the HD219134 system. Sound waves propagating through the stellar interior were used to measure its age and size, and characterize the planets orbiting the star. Credit: openAI, based on original artwork from Gabriel Perez Diaz/Instituto de Astrofísica de Canarias. The 10-second audio clip transforms the oscillations of HD219134 measured using the Keck Planet Finder into audible sound. The star pulses roughly every four minutes. When sped up by a factor of ~250,000, its internal vibrations shift into the range of human hearing. By “listening” to starlight in this way, astronomers can explore the hidden structure and dynamics beneath the star’s surface. Credit: W. M. Keck Observatory
Previously, scientists had captured “stellar songs” mainly from stars hotter than the Sun, using NASA space telescopes such as Kepler and TESS. However, the subtle vibrations of HD 219134, a cooler orange star located just 21 light-years away, are too faint to detect through the brightness changes that space telescopes typically monitor.
To overcome this, researchers turned to Keck Observatory’s KPF instrument, which can detect tiny shifts in the star’s surface motion as it moves toward and away from Earth. Over four consecutive nights, the team gathered more than 2,000 highly precise velocity readings, allowing them to directly observe the star’s oscillations. This marks the first time asteroseismic data have been used to determine the age and radius of a cool star with 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
By analyzing the oscillations observed in HD 219134, the researchers calculated its age to be 10.2 billion years—more than twice as old as the Sun. This places it among the oldest known main-sequence stars whose age has been measured through 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.”
Reference: “K Dwarf Radius Inflation and a 10 Gyr Spin-down Clock Unveiled through Asteroseismology of HD 219134 from the Keck Planet Finder” by Yaguang Li, Daniel Huber, J. M. Joel Ong, Jennifer van Saders, R. R. Costa, Jens Reersted Larsen, Sarbani Basu, Timothy R. Bedding, Fei Dai, Ashley Chontos, Theron W. Carmichael, Daniel Hey, Hans Kjeldsen, Marc Hon, Tiago L. Campante, Mário J. P. F. G. Monteiro, Mia Sloth Lundkvist, Nicholas Saunders, Howard Isaacson, Andrew W. Howard, Steven R. Gibson, Samuel Halverson, Kodi Rider, Arpita Roy, Ashley D. Baker, Jerry Edelstein, Chris Smith, Benjamin J. Fulton and Josh Walawender, 6 May 2025, The Astrophysical Journal.
DOI: 10.3847/1538-4357/adc737
Never miss a breakthrough: Join the SciTechDaily newsletter.
