Double debris disk orbiting a dead star hints at our solar system's future

Astronomers using the European Southern Observatory's Very Large Telescope (ESO's VLT) have found a rare disk of debris around a dead star that provides a glimpse of what may happen to our solar system. Unlike in similar systems previously found, the debris—the leftovers of planets that once orbited the star—is organized in a double disk, the two parts separated by a clear gap. The disk appears to be shaped by two planetary bodies, one possibly as big as Pluto, that have survived the violent death of the star.

"We have known for some time that planets may survive beyond the transformation of their central star, but this is the first example of a complex system with a double debris disk and potentially two surviving planetesimals," says Nicola Gentile Fusillo, an astronomer at the Università degli Studi di Trieste, Italy, and lead author of the study published this week in Nature Astronomy. The central star of this system is the white dwarf J1328−1450, the dense and burned-out core left behind when a star similar to our sun ran out of fuel.

Two rings shaped by surviving bodies

As stars like the sun enter the final stages of their lives, they expand and shed their outer layers, engulfing and destroying nearby planets. The surviving rocky bodies can break apart, forming a disk around the central, dead star. However, the disk around J1328−1450 is different from those observed around other dead stars: instead of having only one ring of vaporized planetary rubble, the star is surrounded by two concentric debris rings.

"The structure we see in this system is particularly intriguing because the two gaseous rings are remarkably stable and remain separated by a gap," says co-author Felipe Lagos-Vilches, an astronomer at the University of Warwick, U.K., and at the Universidad Técnica Federico Santa María in Chile.

"The system is a rare glimpse of the violent, chaotic process by which a planetary system meets its end, and it hints that dead stars can have disk structures far more complex than previously realized," adds Gentile Fusillo, who is also affiliated with the INAF-Astronomical Observatory of Trieste.

According to the team, this complex double structure is likely maintained by two surviving planet-like bodies, on separate orbits. They estimate that the one in the inner ring is the size of a typical asteroid, a few kilometers in diameter, while the outer one could be as large as Pluto, or even our moon.

Distinct chemical signatures in the rings

All known debris disks around white dwarfs have been identified by the same observational signature, which indicates the presence of a single, flat, rotating disk. But the new observations, made with the X-Shooter instrument on ESO's VLT in Chile's Atacama Desert, show that the J1328−1450 system breaks this pattern completely, revealing instead the unique fingerprint of a double disk.

The observations also reveal that elements such as calcium, oxygen, magnesium and iron are present in the disk, indicating a composition similar to that of rocky planetary material found in our own solar system. Moreover, the data indicate that the two rings in the disk in fact have rather different compositions, with the inner ring rich in magnesium gas and the outer largely stripped of it. This suggests that the planetesimals that feed the rings originated from two planets with different compositions. An alternative explanation is that they are the result of different parts of a celestial body, like the crust and core of a planet.

Our solar system could meet a similar end, as our sun will, in the distant future, become a white dwarf in a process that may destroy Earth. "The system therefore offers a remarkable glimpse of what the future of planetary systems, including systems like our own, might look like," concludes Lagos-Vilches.