Using the Chile-based European Southern Observatory’s Very Large Telescope (VLT), a team of astronomers observed a scar on the white dwarf’s surface that was caused by metallic remnants of planets or asteroids, according to a study published this Monday (2/26/2024) by The Astrophysical Journal Letters.
Stars up to eight times the mass of our Sun seem destined to end up as white dwarfs. These stars eventually burn all the hydrogen they use as fuel. Gravity then causes them to collapse and shed their outer layers in the “red giant” phase, eventually leaving behind a compact core: a white dwarf.
Why is a white dwarf a “cannibal”?
Astronomers have found that white dwarfs ingest debris from nearby planets, moons or asteroids, which is why these stars are said to be “cannibalizing pieces of their planetary systems,” lead author Stefano Bagnulo, an astronomer at Armagh Observatory and Planetarium.
In a new study, scientists have discovered for the first time a telltale sign of this process: a scar on the surface of a white dwarf formed by the metallic elements of a planetary fragment or asteroid that it swallowed – scientifically speaking. – and that they were trapped in the star’s magnetic field.
For the authors, this scar on a star located 63 light-years from Earth is a surprise: “We did not think that the magnetic field could prevent the mixing of accumulated material on the surface of the star,” adds Bagnulo.
Metals that have been captured
It is not clear what exact object caused this scar, but experts suggest that this “sandwich planet” contained iron, nickel, titanium, chromium, magnesium and other elements.
Jay Farihi, an astronomer at University College London and co-author of the study, believes the object that left the scar is “as massive as Vesta, the second largest asteroid in our solar system,” which is 530 kilometers in diameter.
“Planetary systems are born together with their star, all condensing from a cloud of dust and gas. We often call a star ‘father’, so it’s a bit like a mother eating her children,” Add.
An atmosphere “contaminated” by metals
This white dwarf began life as a star twice the mass of the Sun and lived for about 1.2 billion years before entering its death throes. Many white dwarfs have a debris disk around them, or the remnants of a planetary system, material that gradually falls to the star’s surface.
“We say that the atmospheres of these stars are ‘contaminated’ by metallic elements,” says Bagnulo.
Strong magnetic field
About 20% of white dwarfs have strong magnetic fields. This observed star has both properties: it has an atmosphere contaminated with metallic elements and is permeated by a strong magnetic field.
“The key discovery is that we saw that the magnetic field plays a central role in how the debris of the disk hits the surface of the star. The material is not only guided by the magnetic field, but also trapped in the magnetic poles.” , without mixing on the surface of the star,” emphasizes Bagnulo.
The future of our solar system
It may not seem like it, but the end of a white star is something much more important than you think, especially with regard to the future of our solar system. The sun is about 4.5 billion years old, but this star has many years left before it collapses.
“Our Sun will become a white dwarf within 5 billion years. And it will probably be contaminated by our planetary system,” concludes Farihi.
JU (rtre, Science Alert, The Astrophysical Journal)
