Dead Star Wears Two Rings of Shattered Planets, Hinting at Our Sun's Fate

Astronomers have found a dead star encircled by two separate rings of planetary wreckage, a structure never before seen around a star of this type. The system, called J1328−1450, may offer a glimpse of what could happen to our own Solar System billions of years from now, according to the European Southern Observatory, as reported by ScienceDaily.

The team suspects that two small surviving bodies, one possibly as large as Pluto or the Moon, keep the rings apart. Neither body has been observed directly.

What exactly did astronomers find?

J1328−1450 is a white dwarf, the dense exposed core left when a star similar to our Sun runs out of fuel. Debris discs have been seen around other white dwarfs, but those appear as a single ring of vaporized planetary material. This one has two concentric rings, one farther from the star than the other, with a clear gap between them.

The results were published in the journal Nature Astronomy. The lead author is Nicola Gentile Fusillo of the Università degli Studi di Trieste in Italy.

How was it detected?

The observations came from the X-Shooter instrument on the European Southern Observatory's Very Large Telescope in Chile's Atacama Desert. The instrument splits light across a broad range of wavelengths, which lets researchers study both the chemical makeup and the motion of material around distant objects.

Debris discs around white dwarfs normally leave a recognizable signature in that light, consistent with one flat, rotating disc. J1328−1450 breaks the pattern. Its light carries the fingerprint of a double disc instead.

What is keeping the rings apart?

The researchers suspect two surviving planetary bodies, each on its own orbit, maintain the gap. They are called planetesimals, a term for smaller solid bodies tied to the formation and evolution of planetary systems.

The one linked to the inner ring is thought to be about the size of a typical asteroid, only a few kilometers across. The one linked to the outer ring could be far larger, potentially reaching the size of Pluto or the Moon. Their gravity could explain why the debris stays in two distinct rings rather than spreading into one disc. Because the objects have not been seen, this remains an inference from the observations.

Co-author Felipe Lagos-Vilches, who works at the University of Warwick in the U.K. and at the Universidad Técnica Federico Santa María in Chile, said the two gaseous rings are remarkably stable and stay separated by a gap.

What is the debris made of?

The astronomers detected calcium, oxygen, magnesium and iron, elements common in rocky planetary material in our Solar System. That indicates the rings hold remnants of solid bodies and not just gas from the star itself.

The two rings differ in chemistry. The inner ring contains substantial magnesium gas, while the outer ring is largely depleted of it. One explanation is that the rings came from separate planets with different compositions, so the system may preserve evidence of more than one destroyed world. Another is that both rings come from different layers of a single planet, for example an outer crust in one ring and deeper material, such as the core, in the other.

Why does it matter?

When a Sun-like star swells and sheds its outer layers, it can engulf planets orbiting too close. More distant rocky objects can survive that upheaval, though gravitational disturbances may later tear some apart and leave debris around the remnant star. J1328−1450 shows a late stage of that process in unusually fine detail.

Gentile Fusillo described the system as “a rare glimpse of the violent, chaotic process” by which a planetary system ends. He said it suggests dead stars can have disc structures far more complex than scientists realized. Either chemical explanation would also give insight into how rocky worlds are destroyed and what they were made of.

For the general reader, the finding is a window into the possible long-term fate of planetary systems like ours, on a timescale of billions of years. It does not describe anything that would affect life on Earth in the foreseeable future.

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Around Prague, based on reporting by ScienceDaily