Metal scar discovered on 'cannibal star'

When a star like our Sun reaches the end of its existence, it can swallow the planets and asteroids surrounding it. Using the Very Large Telescope (VLT) at the European Southern Observatory (ESO) in Chile, researchers have now detected for the first time a visible trace of this process: a scar left on the surface of a white dwarf star (Astrophysical Journal LettersFebruary 26).

Some white dwarfs – the slowly cooling remains of stars like our Sun – are known to eat away parts of their planetary systems. “We have now discovered that the star's magnetic field plays a crucial role in this, creating a scar on the surface of the white dwarf,” says Stefano Pagnolo, an astronomer at Armagh Observatory and Planetarium in Northern Ireland (UK).

The scar the team observed is a concentration of metals on the surface of the white dwarf WD 0816-310, the remains of an Earth-sized star similar to our sun, but slightly larger. “We have shown that these minerals came from planetary debris at least the size of Vesta, which is about 500 kilometers in diameter, and is the second largest asteroid in our solar system,” said co-author Guy Farrehy from University College London. United kingdom).

The observations also provided clues about how the star acquired its metallic scar. The team found that the strength of the metal detection varies with the star's rotation. This suggests that the metals accumulated on a specific portion of the white dwarf's surface, rather than being distributed evenly across the surface. The researchers also found that these variations were coincident with changes in the white dwarf's magnetic field, indicating that the metallic scar is located at one of its magnetic poles. Together, this evidence suggests that the magnetic field directed metals into the star, causing the scar.

Surprisingly, the matter was not evenly distributed over the star's surface, as theory predicted. “Instead, an accumulation of planetary material formed, held in place by the same magnetic field that directed the shattered debris to the star's surface,” said co-author John Landstreet of Western University in Canada. (any)

Original press release