Astronomers observe scar on ‘cannibal’ dwarf star – 02/27/2024 – Science

A slowly cooling stellar ember called a white dwarf, with a scar on its face, is providing new information about the behavior of certain “cannibalistic” stars at the end of their life cycle.

Using the European Southern Observatory’s Very Large Telescope based in Chile, researchers studied a white dwarf located about 63 light years from Earth — a light year is the distance that light travels in one year, 9.5 trillion kilometers. Like all white dwarfs, it is incredibly dense, packing about 70% of the Sun’s mass into an Earth-sized object.

Stars up to eight times the mass of our Sun appear destined to become white dwarfs. They eventually end up burning all the hydrogen they use as fuel. Gravity then causes them to collapse and explode their outer layers into a “red giant” stage, leaving a compact core — the white dwarf.

Astronomers have discovered that white dwarfs ingest fragments of planets, moons and asteroids. In the new study, researchers detected for the first time a telltale sign of this process: a scar on the surface of the white dwarf made up of metallic elements from a planetary fragment or asteroid that it swallowed —accretion, in scientific terms— after being funneled by the magnetic field. of the star.

The researchers were surprised by the discovery because they suspected the debris would mix with the rest of the material on the white dwarf’s surface.

“We didn’t think the magnetic field could stop material from mixing on the star’s surface. When you put sugar in a glass of water, all the water becomes sweet,” said astronomer Stefano Bagnulo of the Armagh Observatory and Planetarium in Ireland. do Norte, main author of the study published this Monday (26) in the Astrophysical Journal Letters.

This white dwarf began its life as a star about twice the mass of the Sun and had a lifespan of perhaps 1.2 billion years before it began its death throes.

Many white dwarfs have a debris disk in their orbit — the remains of a planetary system. This material gradually falls to the star’s surface.

“We say that the atmosphere of these stars is polluted by metallic elements,” said Bagnulo.

About 20% of white dwarfs have a strong magnetic field. Some white dwarfs, like this one, have both characteristics — an atmosphere polluted by metallic elements and are permeated by a magnetic field.

“The key discovery is that we saw this magnetic field play a central role in the way the debris disk falls to the star’s surface. The material is not only channeled by the magnetic field, but also gets trapped at the magnetic poles, without mixing at the surface of the star”, said Bagnulo.

This grim vision of the end of a star may be more than merely academic for us earthlings. It could be a vision of the future of our own Solar System — albeit many, many years away. The Sun is about 4.5 billion years old.

“Our Sun will become a white dwarf in five billion years,” said study co-author and University College London astronomer Jay Farihi, “and will likely be polluted by our planetary system.”