In Hawai‘i, scientists have tuned into the vibrations of a nearby star—and what they heard rewrites the music sheet of the universe.
The star, HD 219134, is a dim, orange orb nestled just 21 light-years away. To the naked eye, it’s unremarkable. Just another star in the night sky. But through the lens of the Keck Planet Finder (KPF), a powerful instrument perched atop Maunakea, it has become a time capsule—and a tuning fork—for understanding how stars live and age.
Listening to Light
Sound can’t propagate in space because there are no atoms or molecules to carry an acoustic wave. But that doesn’t mean stars don’t vibrate. They do—subtly, rhythmically, almost imperceptibly. These oscillations ripple through the stellar body like waves through a bell. To human ears, they are silent. But to astronomers, equipped with precision tools, they are quite revealing.
“The vibrations of a star are like its unique song,” said Yaguang Li, lead author of the new study published in The Astrophysical Journal. “By listening to those oscillations, we can precisely determine how massive a star is, how large it is, and how old it is.”
This technique, known as asteroseismology, has mostly been used to eavesdrop on hotter, more tempestuous stars. HD 219134, however, is a cooler and quieter K-type dwarf. For years, it was thought too subdued to be studied this way.
That changed when Li and his team used KPF to capture over 2,000 ultra-precise velocity measurements across four consecutive nights. Unlike space telescopes that track brightness dips caused by stellar pulsations, KPF measures the physical wobble of the star’s surface—its breath, in essence, moving toward and away from Earth.
The result: the first-ever asteroseismic age and radius of a cool star, derived from its motion.
The Sun’s Senior
The vibrations revealed that HD 219134 is 10.2 billion years old—more than twice the age of our Sun.
This ancient age helps settle a longstanding astrophysical debate. Astronomers typically estimate stellar ages using gyrochronology from the rotation period. Young stars spin fast and slow down as they age. But for stars like HD 219134, that deceleration mysteriously stalls after billions of years.
“This is like finding a long-lost tuning fork for stellar clocks,” said Li. “It gives us a reference point to calibrate how stars spin down over billions of years.”
By anchoring the models at the far end of a star’s lifetime, this discovery allows astronomers to recalibrate stellar aging techniques that once faltered in deep time.
Daniel Huber, a co-author of the study, put it in perspective: “When we find life on another planet, we will want to know how old that life is. Listening to the sounds of its star will tell us the answer.”
But What About Its Planets?
Any alteration in the host star’s size or mass has cascading effects on how we interpret its orbiting planets. HD 219134 is a mini planetary system unto itself, home to five known worlds. Two of them—HD 219134 b and c—are rocky, Earth-sized planets in tight orbits, completing their years in just over three and six days, respectively.
With the new stellar measurements, the team revised the planets’ estimated properties. Planet b now clocks in at 1.54 Earth radii and 4.59 Earth masses, while planet c measures 1.46 Earth radii and 4.23 Earth masses. These values support rocky compositions similar to our own planet.
The improved estimates make HD 219134 a tantalizing benchmark system. As astronomers continue hunting for potentially habitable worlds, refining our knowledge of small, quiet stars like this one is essential.
The Case of the Shrinking Star
The vibrations of HD 219134 also revealed something peculiar. Its size, inferred from asteroseismic data, is about 4% smaller than what previous measurements had shown using a method called interferometry. That may sound negligible, but in the delicate realm of astrophysics, it’s a red flag.
That 4% discrepancy in the star’s radius remains an unresolved thorn. Could magnetic activity be puffing the star up? Probably not—HD 219134’s surface magnetic field is only 2.5 gauss, similar to the Sun. Tidal heating from the nearby planets? Also too weak to matter. Variations in model assumptions? All tried and tested, and none sufficient to explain the gap.
Even the mixing-length parameter, which governs how energy is transported through a star’s convective outer layer, proved inadequate. Increasing it to reconcile the seismic and interferometric radii led to physically implausible helium abundances.
In other terms, tweaking the model to fix the size mismatch ended up breaking the physics elsewhere.
“This suggests that the two methods may not be strictly compatible,” the researchers admit. The asteroseismic method derives the radius from models that match internal structure, while interferometry measures the physical diameter of the star’s glowing disk. Perhaps these methods are measuring subtly different things—or perhaps there’s still physics missing from our models.
The significance of HD 219134 lies in its regularity. It’s a stable, nearby star. It’s not flaring, spinning wildly, or doing anything particularly flashy. And yet, with instruments precise enough to detect oscillations just a few centimeters per second, this K dwarf has become a new cornerstone in the study of stellar aging.
Its quiet rhythm may one day help decode the ticking clocks of countless other stars—and the rocky planets that orbit them.
