White Dwarf Caught Devouring a Rocky World — A Chilling Preview of the Sun’s Distant Fate

White Dwarf Caught Devouring a Rocky World — A Chilling Preview of the Sun’s Distant Fate

A team using the W. M. Keck Observatory on Mauna Kea, Hawaiʻi, has observed a striking case of stellar cannibalism: the hydrogen-atmosphere white dwarf LSPM J0207+3331 is actively accreting debris from a shattered rocky planet. The star lies about 145 light-years away in the constellation Triangulum.

High-resolution spectra reveal 13 heavy elements in the white dwarf's photosphere — the largest number ever detected in a cool, hydrogen-rich white dwarf. Those elements are chemical fingerprints of a disrupted, differentiated body at least ~200 kilometers (about 120 miles) across, with a substantial metallic core and rocky mantle.

Lead author Érika Le Bourdais (University of Montréal) says the event — occurring more than three billion years after the star became a white dwarf — “challenges our understanding of planetary system evolution.” The discovery also offers a sobering look at the distant future of planetary systems like our own, more than five billion years from now when the Sun becomes a white dwarf.

Why this detection is surprising

Hydrogen-rich white dwarf atmospheres are relatively opaque, and heavy elements normally sink out of view on timescales of days. By contrast, helium-atmosphere white dwarfs (which are more transparent) can retain detectable metals for millions of years, making them historically easier targets for such studies. Finding 13 elements in a cool, hydrogen-dominated dwarf is therefore unexpected and scientifically valuable.

What the elements reveal

From the observed abundance pattern, researchers estimate the destroyed object had a high core-mass fraction of roughly 55% — significantly larger than Earth’s (~32%) but lower than Mercury’s (~70%). That composition implies the body was internally differentiated with a large metallic core, offering direct evidence of rocky-planet structure long after the host star died.

How it may have happened

Co-author John Debes (Space Telescope Science Institute) notes, “Something clearly disturbed this system long after the star’s death.” Possible triggers include orbital instabilities produced when the star lost mass during late stellar evolution, or gravitational nudges from surviving planets — for example, distant, cold giant planets analogous to Jupiter. Such companions would be hard to detect directly but could have slowly scattered the smaller body onto a star-grazing orbit.

Researchers plan to search for indirect evidence of massive companions using archival data from ESA’s Gaia mission and infrared observations from NASA’s James Webb Space Telescope. Combined data could identify culprits and illuminate long-term multi-planet dynamics in dead systems across the galaxy.

Why it matters

This discovery opens a new window on the long-term evolution and ultimate fate of planetary systems. When planets are torn apart and accreted by white dwarfs, their chemical fingerprints become accessible — providing rare, direct measurements of exoplanetary composition and interior structure that are otherwise impossible to obtain.

Publication: The study appears in The Astrophysical Journal.

Instruments & data: W. M. Keck Observatory spectroscopy; future follow-up may use Gaia archival astrometry and JWST infrared imaging/spectroscopy.