Astronomers watch a dead star eat what’s left of its planet

A dead star is tearing into the leftovers of its own planetary system. The feast shows up as 13 rock-forming elements in the star’s light, and the ruined body was at least 120 miles wide.

The star sits in a nearby patch of sky and was observed with one of the world’s sharpest telescopes in Hawaii. The result is a crisp look at how old systems can still change long after the parent star fades.

Dead star feasts on debris

In a new study, astronomers describe their fascinating observations. A cool, hydrogen-rich white dwarf called LSPM J0207+3331 can be seen swallowing debris from a rocky body.

The observations relied on high-precision spectroscopy from Keck’s HIRES instrument to isolate faint metal lines.

“This discovery challenges our understanding of planetary system evolution,” said lead researcher Érika Le Bourdais from the University of Montréal’s Trottier Institute for Research on Exoplanets (IREX).

A white dwarf – a dense stellar remnant with crushing surface gravity – is what a Sun-like star becomes after burning its fuel. Most are quiet, yet some show heavy elements that should sink quickly.

Spectral signatures from several heavy elements reveal material typical of rocky crust and dense planetary cores, showing the star is still feeding on its former worlds.

Ancient clues from a dead star

Astronomers use spectroscopy – a technique that splits light to read elemental barcodes – to turn a star into a lab bench. This is the central promise of polluted white dwarfs.

Hydrogen-rich atmospheres usually hide metals, which makes this detection stand out. “The amount of rocky material is unusually high for a white dwarf of this age,” said Patrick Dufour of the Université de Montréal.

The metals sit in the photosphere, thin visible layer where starlight escapes. In hydrogen-rich stars that layer mixes quickly, so ongoing infall must constantly refresh the signal.

The debris did not simply graze the star and pass by. The object left a warm belt of dust around the star from when it crossed into the Roche limit.

This limit marks the distance from a celestial body within which a smaller, self-gravitating object would be torn apart by the larger body’s tidal forces.

Rock that’s being ground into dust

“Something clearly disturbed this system long after the star’s death,” said John Debes from the Space Telescope Science Institute. Something kicked a remnant inward only a few million years ago. 

Many polluted white dwarfs show steady feeding across billions of years. That staying power means some systems keep a long lived supply of debris.

Back in 2019, observers flagged an infrared glow from this very star. The new spectrum links that glow to fresh rock being ground to dust.

Surviving outer planets could be the culprits that scatter rubble inward. Gaia’s precise astrometry can reveal such giants.

Planet’s metal heart exposed

The chemistry looks mostly Earth-like, but with a tilt toward iron, nickel, and cobalt. That tilt points to a differentiated, layered world with a metal core and rocky mantle.

The enhanced iron group elements are siderophile, or iron-loving, elements that prefer to reside in metallic cores. Their boost suggests the parent body was stripped to its deeper layers before disruption.

The team’s model favors a high core-mass fraction for the parent body. The pattern also shows very low carbon, which fits a dry, rocky source rather than icy leftovers.

The white dwarf’s atmosphere even shows faint emission lines in calcium. This hint of activity suggests gentle heating high above the visible layers.

Warm debris circles the star

The star’s mid-infrared light carries a strong silicate signature. Earlier work with Spitzer found such mineral features in similar disks.

A single inner disk of dust can explain the latest data. That disk likely formed when the incoming body shattered and spread into a thin, hot ring.

Silicate-rich dust brightens near ten microns and cools steadily outward. As grains collide, they grind down and leak gas that can briefly glow.

The dead star keeps dining

This star is about 145 light years away and roughly three billion years old. The ongoing meal shows that planetary systems do not simply freeze after the star’s quiet phase.

Heavy element pollution sinks quickly under strong gravity. Ongoing delivery is the only way to keep those elements detectable for long.

Hydrogen-rich white dwarfs are common, yet they are usually harder places to spot many elements. The new detection expands where astronomers look for the chemistry of ancient worlds.

Keck Observatory’s HIRES instrument captured the key fingerprints with high resolution. The data allow researchers to model the convection zone – churning layer where newly arrived metals mix before sliding deeper.

Future observations of the dead star

Infrared instruments can read the dust in finer detail and test whether a single ring fits. JWST can trace the exact minerals, while wide surveys can check how often old stars keep eating.

Future ultraviolet and infrared spectra could tighten oxygen limits and nail down water content. Tighter limits would refine the total mass and the depth of the missing outer layers.

Gaia and ground-based infrared telescopes can hunt for surviving gas giants far from the star. If found, those giants would be the prime suspects that stir the debris and feed the disk.

This system provides a clear test case for delayed instability models that come into play long after a star’s death. Comparing its chemistry and disk structure to those predictions could refine our understanding of long-term planetary dynamics.

Image credit: NASA, ESA, Joseph Olmsted (STScI)

The study is published in The Astrophysical Journal Letters.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–