There are still 5 billion years to go, but one day the Sun will say goodbye with some cosmic fireworks. When a star like our Sun reaches the end of its life, it can swallow up the surrounding planets and asteroids that were born with it. The sun swells and becomes a red giant engulfs the orbits of Mercury, Venusand probably Earth too. This is known to occur, but until now the traces left on a star by its planetary feast were unknown.
Now, thanks to the European Southern Observatory’s Very Large Telescope (ESO VLT) in Chile, a team of scientists led by Stefan Bagnul has for the first time found the only signature of this process: a scar imprinted on the surface of a white dwarf. The results were published in The Astrophysical Journal Letters.
“Certain white dwarfs, slowly cooling the embers of stars like our Sun, have been shown to cannibalize parts of their planetary systems,” Bagnulo explained in a statement. We have now found out that the star’s magnetic field plays a key role in this process, which results in a scar on the surface of the white dwarf.”
The scar the team observed is a concentration of metals imprinted on the surface of the white dwarf WD 0816-310, the remnant of an Earth-sized star similar to our Sun, located about 60 light years from Earth. “We show that these metals come from a planetary fragment as large as or possibly larger than Vesta, which is about 500 kilometers in diameter and is the second largest asteroid in the Solar System,” adds Jay Farihi, co-author of the study.
Observations made with the VLT have also provided a clue How the star got his “metallic scar”. The team noticed that the metal detection levels changed as the star rotated, suggesting that the metals are concentrated in a specific region of the white dwarf’s surface, rather than spread across it. They also found that these changes were synchronized with changes in the magnetic field white dwarf, suggesting that this metallic bump is located at one of its magnetic poles. Taken together, all of these clues suggest that the magnetic field directed the metals toward the star, and that’s what would have created its imprint.
Previously, astronomers observed many metal-contaminated white dwarfs scattered across the star’s surface. They are known to come from disturbed planets or asteroids that get too close to the star, however, in the case of WD 0816-310The team believes that the vaporized material was ionized and driven toward the magnetic poles by the white dwarf’s magnetic field. The process shares similarities with how auroras form on Earth, only they leave an indelible mark on the star.
“Surprisingly material it did not mix evenly on the surface of the star, as predicted by the theory – confirmed by John Landstreet, also the author of the study -. Instead, this scar is a concentrated chunk of planetary material, held in place by the same magnetic field that steered the debris the star would absorb. “Nothing like this has been seen before.
To reach these conclusions, the team used the tool FORS2, spol swiss army knife of luck in VLT which allows to acquire images and also works in polarimetry, spectroscopy and multi-object, that is, it allows to analyze composition, distances, cycles and other variables with the same instrument.
Thanks to FORS2, the authors of the study were able to detect the metal scar and connect it to the star’s magnetic field. “ESO has the unique combination of capabilities needed to observe faint objects such as white dwarfs and sensitively measure stellar magnetic fields,” says Bagnulo.
Thanks to these observations, astronomers can reveal the general composition of exoplanets, planets that orbit other stars outside the Solar System. This unique study also shows how planetary systems can remain dynamically active even after their ‘death’.
