Dr Stefano Bagnulo, an astronomer based in the Armagh Observatory, was lead author of the study that used observations from the VLT in Chile for the discovery.

An astronomer based in Ireland has led a study that discovered how a metallic ‘scar’ on the surface of a distant white dwarf is made up of remnants of an object in its planetary system.

A white dwarf is what remains after stars around the size of our sun end their life cycle. But before transitioning from a star to a white dwarf, these stars cannibalise planets and other objects in their respective planetary systems. Now, scientists have made an interesting discovery.

“It is well known that some white dwarfs – slowly cooling embers of stars like our sun – are cannibalising pieces of their planetary systems,” said Dr Stefano Bagnulo, lead author of the study published in The Astrophysical Journal Letters.

“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.”

Bagnulo is an astronomer at Armagh Observatory and Planetarium in Northern Ireland. Using the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile, the team discovered the scar on WD 0816-310, a white dwarf that is about the size of Earth but was once part of a star more massive than our sun.
The scar that the team observed – with the help of what the team calls a “Swiss army knife” instrument on the VLT called FORS2 – is a concentration of metals imprinted on the white dwarf’s surface.

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

“We have demonstrated that these metals originate from a planetary fragment as large as or possibly larger than Vesta, which is about 500km across and the second-largest asteroid in the solar system,” said co-author Jay Farihi, a professor at University College London.

The team said that the latest observations also provide clues to how the star got its metal scar in the first place. Scientists 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.
These changes, the team said, were synchronised with changes in the white dwarf’s magnetic field, indicating that this metal scar is located on one of its magnetic poles.

“Surprisingly, the material was not evenly mixed over the surface of the star, as predicted by theory,” added co-author John Landstreet, a professor at Western University in Canada. Landstreet is also affiliated with the Armagh Observatory and Planetarium.

“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.”

Vish Gain

This article originally appeared on www.siliconrepublic.com and can be found here.