In a celestial revelation, astronomers using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile have uncovered a cosmic signature—a scar etched on the surface of a white dwarf star, offering a unique glimpse into the dramatic end of a star’s life. When stars, like our Sun, approach the conclusion of their existence, they engage in a process of ingesting surrounding planets and asteroids. This study, published in The Astrophysical Journal Letters, marks the first-time detection of a distinctive aftermath of this cosmic feast.
Lead author Stefano Bagnulo, an astronomer at Armagh Observatory and Planetarium, reveals, “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.” The scar was observed on the white dwarf WD 0816-310, an Earth-sized remnant of a star similar to our Sun but slightly more massive.
The scar itself is a concentration of metals on the surface of the white dwarf, revealing an intricate dance between a star’s magnetic field and the remnants of its planetary system. Professor Jay Farihi from University College London, co-author of the study, emphasizes the origin of these metals, stating, “We have demonstrated that these metals originate from a planetary fragment as large as or possibly larger than Vesta, which is about 500 kilometers (~300 miles) across and the second-largest asteroid in the Solar System.”
What makes this discovery even more intriguing is the revelation that the scar is not uniformly spread over the star’s surface, as theoretical predictions suggested. Instead, it appears as a concentrated patch of planetary material, intricately held in place by the magnetic field that guided these fragments in their descent onto the white dwarf. Co-author John Landstreet, a professor at Western University, Canada, and affiliated with the Armagh Observatory and Planetarium, notes, “Nothing like this has been seen before.”
The team leveraged the capabilities of the VLT’s FORS2 instrument, often referred to as a ‘Swiss-army knife,’ to detect and connect the metal scar to the white dwarf’s magnetic field. The observations, complemented by archival data from the VLT’s X-shooter instrument, provide unprecedented insights into the magnetic choreography and metal concentration on the white dwarf’s surface.
Not only does this study deepen our comprehension of white dwarfs, but it also showcases the enduring dynamism of planetary systems even after the host star’s demise. Furthermore, the observations hint at the potential to unravel the composition of exoplanets, offering astronomers a rare opportunity to explore the planetary makeup of distant star systems.
