By analyzing subtle stellar vibrations,
researchers using the Keck Planet Finder uncovered hidden interior
structures that challenge long-standing models
Maunakea, Hawaiʻi – 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 (KFP), 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.
Maunakea, Hawaiʻi – 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 (KFP), 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 towards 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.”
Keck Observatory’s KPF instrument precisely measures the motion of the stellar surface towards 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.”
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.
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.”
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.
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.”
Paper DOI: 10.3847/1538-4357/adc737Source: W.M. Observatory/Science News
Media Contact
Meagan O’Shea
moshea@keck.hawaii.edu
About KPF
The Keck Planet Finder (KPF) is a high-resolution optical spectrometer
designed to study exoplanets identified through the behavior of their
host stars using the Doppler Technique – a method that can detect stars
moving back and forth at a rate of less than 30 centimeters per second.
KPF has the ability to study smaller, Earth-like planets orbiting nearby
bright stars and the ability to characterize transiting planets from
missions such as TESS, Kepler, and PLATO, measuring their masses and
orbital properties. Support for KPF was provided by the National Science
Foundation, the Heising-Simons Foundation, W. M. Keck Foundation,
Simons Foundation, Mt. Cuba Astronomical Foundation, the Jet Propulsion
Laboratory, which is managed by Caltech for NASA, private donors, and W.
M. Keck Observatory, Caltech, University of California, and University
of Hawaiʻi.
ABOUT W.M. Keck Observatory
The W. M. Keck Observatory telescopes are among the most scientifically
productive on Earth. The two 10-meter optical/infrared telescopes atop
Maunakea on the Island of Hawaii feature a suite of advanced instruments
including imagers, multi-object spectrographs, high-resolution
spectrographs, integral-field spectrometers, and world-leading laser
guide star adaptive optics systems. Some of the data presented herein
were obtained at Keck Observatory, which is a private 501(c) 3
non-profit organization operated as a scientific partnership among the
California Institute of Technology, the University of California, and
the National Aeronautics and Space Administration. The Observatory was
made possible by the generous financial support of the W. M. Keck
Foundation. The authors wish to recognize and acknowledge the very
significant cultural role and reverence that the summit of Maunakea has
always had within the Native Hawaiian community. We are most fortunate
to have the opportunity to conduct observations from this mountain. For
more information, visit: www.keckobservatory.org
