Astronomers Find a Dead Star Ringed by Two Debris Disks, Shaped by Surviving Planetesimals

Astronomers using the European Southern Observatory's Very Large Telescope have found a rare disk of debris around a dead star that offers a glimpse of what may happen to our own solar system. Unlike similar systems found before, the wreckage of planets around this star is organized into a double disk, its two parts separated by a clear gap.

The star is the white dwarf J1328-1450, the dense, burned-out core left behind when a star similar to our sun ran out of fuel. The disk appears to be shaped by two planetary bodies, one possibly as big as Pluto, that survived the violent death of the star. The results were published this week in Nature Astronomy.

"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," said Nicola Gentile Fusillo, an astronomer at the University of Trieste in Italy and lead author of the study.

The process that produces such disks is well understood in outline. As stars like the sun enter the final stages of their lives, they swell and shed their outer layers, engulfing and destroying nearby planets. Rocky bodies that survive can break apart, and their remains form a disk around the dead star. The disk around J1328-1450 is different. Instead of one ring of vaporized planetary rubble, the star is encircled by two concentric rings.

The team used the X-shooter instrument on the Very Large Telescope to measure the speed of gas orbiting the white dwarf. The gas moves at two distinct speeds, which indicates it sits in two separate rings with a gap between them. The disk contains both gas and dust. The most likely explanation, the researchers say, is that two planetesimals orbiting the star interact with dust grains and release gas as they go, maintaining each ring.

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

The team estimates that the body in the inner ring is about the size of a typical asteroid, a few kilometers across, while the outer one could be as large as Pluto. Neither object has been seen directly. Their existence is inferred from the structure and motion of the gas.

"The system is a rare glimpse of the violent, chaotic process by which a planetary system meets its end," Gentile Fusillo said, "and it hints that dead stars can have disk structures far more complex than previously realized."

The finding matters for understanding the long-term fate of planetary systems, including ours. In roughly five billion years, the sun is expected to follow the same path. J1328-1450 shows that some small worlds can endure that transformation and keep sculpting the debris around the stellar remnant.