A Dead Star With Two Rings of Debris Shows How Planetary Systems End

Around 1,600 light-years from Earth, in the constellation Virgo, lies a dead star that has kept a little of its old planetary system. Astronomers using the European Southern Observatory's Very Large Telescope have found a white dwarf with two rings of vaporised rocky debris circling it, separated by a clean, empty gap. Nothing like it has been seen before. The team thinks two small worlds survived their star's death and are now feeding the rings. It may be a preview of what our own Solar System could look like billions of years from now.

The star is known by its catalogue name, WD J1328−1450. The study was published this week in Nature Astronomy. Here is what was found, how astronomers saw rings they can't actually photograph, and what it tells us about the Sun's far future.

Quick facts

• Object: white dwarf WD J1328−1450, about 1,600 light-years away in Virgo
• Discovery: two separate, concentric rings of gas made from destroyed rocky bodies
• Instrument: X-shooter spectrograph on ESO's Very Large Telescope, Chile
• Why it's new: every gas disc found around a white dwarf until now had a single ring
• Likely cause: two surviving planetesimals, one asteroid-sized and one possibly as big as Pluto
• Lead author: Nicola Pietro Gentile Fusillo, University of Trieste and INAF

What is a white dwarf?

A white dwarf is the leftover core of a star like the Sun. When such a star runs out of hydrogen fuel, it swells into a red giant and then puffs off its outer layers into space. What remains is a hot, dense core, about the size of Earth but holding roughly half the mass of the Sun. A teaspoon of its material would weigh several tonnes on Earth. It no longer burns fuel. It simply glows and slowly cools over billions of years.

For a long time, astronomers assumed that any planets around such a star would be wiped out during the red giant phase. We now know that is not always true. Many white dwarfs show traces of metals such as calcium and magnesium in their atmospheres. Those elements should sink out of sight quickly, so their presence means something is constantly falling onto the star. The best explanation is rocky debris from asteroids or small planets that wandered too close and were torn apart by the dead star's gravity.

How do you see a ring you can't photograph?

The rings around WD J1328−1450 are far too small and too distant to show up in an image. Instead, the team split the star's light into its colours using X-shooter, a powerful spectrograph. Gas in the disc gives off light at very specific colours, called emission lines.

Here is the clever part. Because the gas is orbiting, one side of the disc moves towards us and the other side moves away. The approaching side shifts its light slightly towards blue and the receding side towards red. A single rotating ring therefore turns each emission line into a double peak. That two-peak shape is what astronomers had seen in every known white dwarf gas disc.

This star showed four peaks instead of two. The only sensible way to get that pattern is to have two rings orbiting at different speeds, with a gap between them. The team watched the system over time, and the two rings stayed stable and clearly separate.

Two rings, two different worlds

The rings are not twins. The gas contains calcium, oxygen, magnesium and iron, the same kind of mix found in rocky bodies in our own Solar System. But the inner ring is rich in magnesium, while the outer ring has very little of it. That difference is an important clue.

According to ESO's announcement, the most likely explanation is that each ring is being fed by its own small body that survived the star's death. The inner one may be only a few kilometres across, about the size of a typical asteroid. The outer one could be as large as Pluto, or even our Moon. As these bodies slowly lose material, their vapour spreads out and keeps each ring topped up.

The team also considered another option: the rings could come from different layers of a single shattered world, such as its crust and its core, which would have different chemistry. Either way, the system shows that a dead star can host more than one surviving rocky body at the same time. Lead author Nicola Pietro Gentile Fusillo said it is the first known example of such a complex system, with a double disc and potentially two surviving planetesimals.

Why this is a glimpse of our own future

In roughly five billion years, the Sun will run low on hydrogen and swell into a red giant. Mercury and Venus will almost certainly be swallowed. Earth may be too, or it may just escape as the Sun loses mass and the planets' orbits drift outward. Eventually the Sun will shed its outer layers and settle down as a white dwarf.

What happens next is exactly what systems like WD J1328−1450 show us. Surviving planets, moons and asteroids can be nudged onto new paths. Any that stray too close to the white dwarf get pulled apart by its gravity and turn into rings of dust and gas. Co-author Felipe Lagos-Vilches of the University of Warwick described the system as a rare view of how a planetary system ends, and a possible stage in the very distant future of our own.

Stars have life stories, and the end of a star's life can look very different depending on its mass. Lighter stars like the Sun become white dwarfs. Much heavier stars end in a supernova, which is what astronomers expect for the red giant described on our Betelgeuse supernova page.

Where is it in the sky?

WD J1328−1450 lies in Virgo, the large constellation whose brightest star is Spica. The white dwarf itself is far too faint to see without a big telescope, but Spica is easy to spot with the naked eye. Our Spica star guide shows where to find it from your location, and the brightest stars page lists other famous stars you can see tonight.

What comes next?

The team wants to watch the system for longer to see whether the rings change over time, and to pin down the sizes and orbits of the bodies inside them. Large surveys now under way are taking spectra of hundreds of thousands of white dwarfs. That should turn up more of these "planetary graveyards" and show how common double rings really are. For more stories like this, follow our upcoming space events and the latest news on SpaceTracker.live.

FAQ

What is special about this white dwarf with two rings?
It is the first white dwarf found with two separate rings of gaseous debris. Every known gas disc around a white dwarf before this had only one ring.

How far away is WD J1328−1450?
About 1,600 light-years from Earth, in the constellation Virgo.

Will the Sun become a white dwarf?
Yes. In billions of years, after a red giant phase, the Sun will shed its outer layers and leave behind a white dwarf about the size of Earth.

Could planets survive around a white dwarf?
Some can. This discovery suggests that at least two rocky bodies survived around WD J1328−1450 and are slowly feeding its debris rings.