Home Science and Nature VLT Detects ‘Metal Scar’ on Surface of White Dwarf Star

VLT Detects ‘Metal Scar’ on Surface of White Dwarf Star

by News7

Dynamically active planetary systems orbit a significant fraction of white dwarf stars. These stars often exhibit surface metals accreted from debris disks. However, the full journey of a planetesimal from star-grazing orbit to final dissolution in the host star is poorly understood. In a new paper in the Astrophysical Journal Letters, astronomers report the discovery that the cool metal-polluted star WD 0816-310 has cannibalized heavy elements from a planetary body similar in size to the dwarf planet Vesta.

An artist’s impression of WD 0816-310, a magnetic white dwarf located 63 light-years away in the constellation of Puppis. Image credit: L. Calçada / ESO.

“It is well known that some white dwarfs — slowly cooling embers of stars like our Sun — are cannibalizing pieces of their planetary systems,” said Dr. Stefano Bagnulo, an astronomer at Armagh Observatory and Planetarium.

“Now we have discovered that the star’s magnetic field plays a key role in this process, resulting in a scar on the white dwarf’s surface.”

The metal scar the team observed on WD 0816-310 is a concentration of metals imprinted on the white dwarf’s surface.

“We have demonstrated that these metals originate from a planetary fragment as large as or possibly larger than Vesta, which is about 500 km across and the second-largest asteroid in the Solar System,” said University College London’s Professor Jay Farihi.

To observe WD 0816-310, the astronomers used the FORS2 instrument on ESO’s Very Large Telescope (VLT).

They also relied on archival data from VLT’s X-shooter instrument to confirm their findings.

The authors noticed that the strength of the metal detection changed as the star rotated, suggesting that the metals are concentrated on a specific area on the white dwarf’s surface, rather than smoothly spread across it.

They also found that these changes were synchronized with changes in the white dwarf’s magnetic field, indicating that this metal scar is located on one of its magnetic poles.

Put together, these clues indicate that the magnetic field funneled metals onto the star, creating the scar.

“Surprisingly, the material was not evenly mixed over the surface of the star, as predicted by theory. 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,” said Western University’s Professor John Landstreet.

“ESO has the unique combination of capabilities needed to observe faint objects such as white dwarfs, and sensitively measure stellar magnetic fields,” Dr. Bagnulo said.


Stefano Bagnulo et al. 2024. Discovery of Magnetically Guided Metal Accretion onto a Polluted White Dwarf. ApJL 963, L22; doi: 10.3847/2041-8213/ad2619

Source : Breaking Science News

You may also like