3 billion-year-old white dwarf still consuming its planetary system challenges previous assumptions

In approximately 5 billion years, the sun will deplete its hydrogen fuel and collapse under its own gravity, becoming a white dwarf. Though Earth-sized, this dense remnant will retain much of the sun’s gravitational influence.

This transformation marks the end of our solar system as we know it. Or does it?

The universe is never idle. Everything is in a perpetual state of fluctuation. Still, it came as a surprise to astronomers to find a 3 billion-year-old white dwarf actively accreting material from its former planetary system—a discovery that challenges assumptions about the late stages of stellar remnant evolution.

The telltale forensic evidence came from observations with the W. M. Keck Observatory on Maunakea in Hawaiʻi. Spectroscopic analysis of light from the dwarf found 13 chemical elements that must have come from a small rocky body—an asteroid or dwarf planet.

Like an apple falling out of a tree, some unknown gravitational disturbance within the past few million years may have sent this object spiraling inward. It was then torn apart by tidal forces and absorbed into the white dwarf’s surrounding debris disk.

Astronomers have identified a rare, ancient planetary system still being actively consumed by its central white dwarf star, LSPM J0207+3331, which is located 145 light-years from Earth. This system hosts the oldest and most metal-rich debris disk ever observed around a hydrogen-rich white dwarf, raising new questions about the long-term stability of planetary systems billions of years after stellar death.

“This discovery challenges our understanding of planetary system evolution,” said lead author Érika Le Bourdais of the Trottier Institute for Research on Exoplanets at Université de Montréal. “Ongoing accretion at this stage suggests white dwarfs may also retain planetary remnants still undergoing dynamical changes.”

Spectroscopic data from the W. M. Keck Observatory on Maunakea in Hawaiʻi revealed the white dwarf’s atmosphere is polluted with 13 chemical elements, an evidence of a rocky body at least 120 miles (200 kilometers) wide that was torn apart by the star’s gravity. “The amount of rocky material is unusually high for a white dwarf of this age,” noted co-author Patrick Dufour, also of Université de Montréal.

Hydrogen-rich atmospheres around white dwarfs typically mask such elemental signatures, making this detection especially significant. “Something clearly disturbed this system long after the star’s death,” said co-investigator John Debes of the Space Telescope Science Institute in Baltimore, Maryland. “There’s still a reservoir of material capable of polluting the white dwarf, even after billions of years.”

Delayed planetary instability

Nearly half of all polluted white dwarfs show signs of accreting heavy elements, indicating their planetary systems have been dynamically disturbed. In the case of LSPM J0207+3331, a recent perturbation— within the last few million years—probably sent a rocky planet spiraling inward. “This suggests tidal disruption and accretion mechanisms remain active long after the main-sequence phase of a star’s life,” said Debes. “Mass loss during stellar evolution can destabilize orbits, affecting planets, comets, and asteroids.”

The system may exemplify delayed instability, where multi-planet interactions gradually destabilize orbits over billions of years. “This could point to long-term dynamical processes we don’t yet fully understand,” Debes added.

Searching for outer planets

Astronomers are now investigating what may have triggered the disruption. Surviving Jupiter-sized planets could be responsible but are difficult to detect due to their separation from the white dwarf and low temperatures. Data from ESA’s Gaia space telescope may be sensitive enough to detect such planets through their gravitational influence on the white dwarf.

NASA’s James Webb Space Telescope could also provide insights by taking infrared observations of the system for signs of outer planets. “Future observations may help distinguish between a planetary shakeup or the gravitational effect of a stellar close encounter with the white dwarf,” said Debes.

These results are published in The Astrophysical Journal Letters.