Astronomers spot metal imprint on 'cannibal' white dwarf star

Astronomers using the European Southern Observatory’s Very Large Telescope have for the first time found evidence of a dying star ingesting material from nearby planets. 

The white dwarf – known as WD 0816-310 – is two steps along its lifecycle from our Sun. 

Eventually – in about 5 billion years or so – the Sun will expand to become a red giant. It will then spend billions more cooling to become a white dwarf, around the size of the Earth. 

During this process, red giants consume material in their vicinity including planets, moons and asteroids.

Now, the ESO has found evidence of this process, saying metallic ‘scarring’ on the surface of the white dwarf is a concentration of heavy metals in one of the star’s polar regions, likely from an orbiting planet about 500km-wide.  

Previously, evidence of metallic ‘pollution’ on white dwarves has been observed as a more even distribution across the surface. 

The findings, published in Astrophysical Journal Letters, suggest the star’s magnetic field is responsible for ripping the metals from the Vesta-like object and depositing them in a single spot. 

John Landstreet, an astronomer attached to Western University, Canada, explains the phenomenon is entirely new to science. He, along with another of the study’s co-authors Stefano Bagnulo, previously identified weak magnetic fields emanating from WD 0816-310 and 3 other white dwarves.  

“The material was not evenly mixed over the surface of the star, as predicted by theory,” says Landstreet. 

“Instead, this scar is a concentrated patch of planetary material, held in place by the same magnetic field that has guided the infalling fragments. Nothing like this has been seen before.”