The VLT telescope has found the remains of a planetary system around a dead star, the debris disk appearing weathered by two planetary bodies, one as large as Pluto. Is this the future of the Solar System?
An international team of astronomers, led by the Universities of Trieste and Warwick, has discovered something never seen before: a dead star surrounded by not one, but two rings of gas separated by empty space. The discovery, published in the journal Nature Astronomygives us an idea of what might one day happen to our Solar System.
What is a white dwarf?
The star in question is called WD J1328−1450 and is located about 1,600 light-years from Earth. It is a white dwarf, that is, what remains of a star like the Sun when its “fuel” runs out. Towards the end of its life such a star swells enormously, sheds its outer layers and can swallow up nearby planets.
But in the end what remains is a small, dull and very dense nucleus: despite having a mass comparable to that of a star, it has dimensions close to those of the Earth. Not everything, however, is destroyed. Asteroids and other rocky bodies survive because at distances where the star’s expansion has not reached them, they can break apart and form a disk of debris around the dead star.
A unique case
Until now, all disks of gas observed around white dwarfs have been single, flat, rotating structures. The 21 similar cases already known all showed the same “signal” with two peaks. This time the observations, made with the X-shooter instrument of the European Southern Observatory’s (ESO) Very Large Telescope in Chile, revealed a signal with four peaks: the signature of two concentric rings separated by a void.
To get an idea of the size, just think of the distance between the Earth and the Moon, around 384,000 kilometres: well the inner ring goes from around 100,000 to 240,000 kilometers from the star, so it remains closer than the Moon is to us; the outer ring starts at around 375,000 kilometers and reaches over 1.3 million kilometres. The observations, repeated between 2021 and 2023, show that the structure has remained stable for more than two years.
What are rings made of
The gas contains calcium, oxygen, magnesium and iron, a mixture similar to that of rocks in our Solar System. The two rings, however, are not the same: the internal one is rich in magnesium, the external one has much less. This suggests that the debris comes from two bodies born in different conditions, or from different layers of a single body.
Two hidden “guardians”.
According to the researchers, keeping this structure tidy could be two surviving planetary bodies, each orbiting within its own ring. As they move through the dust, they would release the gas we observe. They cannot be seen directly, but models suggest that the inner one is small, like an asteroid of a few kilometers, while the outer one could be as large as Pluto or even as large as the Moon.
Nicola Pietro Gentile Fusillo, main author of the study (University of Trieste and INAF-Astronomical Observatory of Trieste), explains it like this: «We cannot directly see the two planetary bodies, but we can deduce their probable presence from the shape and composition of the gas. It’s like reconstructing the architecture of a destroyed planetary system starting from the traces left by its last fragments. For the first time, we can observe that such a complex configuration can survive even around a dead star.”
What does it tell us about the future of our Solar System?
The discovery challenges current theories about how these disks form and evolve and where the gas comes from. It also affects us closely: in a few billion years (estimated around five) the Sun will also become a white dwarf and this process could destroy the Earth (not everyone agrees, however).
Systems like WD J1328−1450 show us that, even after a star’s demise, the remnants of its planets can continue to exist in surprisingly ordered shapes.
