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- By Rebecca Wilson
- BBC News NI
Image source, IT/L. Road
Artist’s impression of the magnetic white dwarf WD 0816-310 with a metallic scar
Armagh astronomers have discovered a sign that a star was feeding on nearby planets and asteroids.
A metal scar found on the surface of the dead star has never been seen before, astronomer John Landstreet said.
It was discovered at the Armagh Observatory and Planetarium astronomical research centre.
The scar, believed to be 500 kilometers (310 miles) long, was on an Earth-sized remnant of a star in a nearby solar system.
The system no longer creates energy in its core, so the star is dead.
Research astronomers named the white dwarf star WD 0816-310.
The research found that the scar developed after the white dwarf ingested surrounding planets and asteroids that were born at the same time, causing a concentration of metals that scar the star’s surface.
Dr. Landstreet, co-author of the research paper, is a member of the team that discovered the first magnetic white dwarf in 1970.
“Surprisingly, the material did not mix uniformly over the star’s surface, as theory predicted,” he said.
“Instead, this scar is a concentrated patch of planetary material, held in place by the same magnetic field that has guided the falling fragments. Nothing like it has been seen before.”
What is a white dwarf?
A white dwarf is the burned-out remains of a dead star, something our Sun will become in about five billion years.
When a star dies, gravity means that heavier elements move towards the center, while lighter elements, such as hydrogen or helium, rise to the outer shell.
At their hottest, stars will have hydrogen atmospheres, but as they cool over time, they tend to have helium atmospheres.
But typical white dwarfs don’t have one side of the star dedicated to one element and the other dominated by another.
At 500 kilometers long, the star is about the same size as Vesta, the second largest asteroid in our solar system.
Image source, IT/L. Road
The research used the Very Large Telescope (VLT) of the European Southern Observatory, based in Chile.
Astronomers said the strength of the metal detection synchronized with observed changes in the star’s magnetic field, leading the team to determine that the metal scar was located at one of the star’s magnetic poles.
This showed that the metals were channeled into the star by its magnetic field, creating the scar.
Stefano Bagnulo, an astronomer at the Armagh Observatory and Planetarium, said it was well known that some white dwarfs were cannibalizing parts of their planetary systems.
“We have now discovered that the white dwarf’s magnetic field plays a key role in this process, causing a scar on its surface,” he said.