An international group of astronomers, coordinated by researchers from the University of Trieste and the University of Warwick, has reported the discovery of a unique celestial structure: a dead star encircled not by one, but by two separate gas rings divided by an empty space. Published in Nature Astronomy, this finding offers new insights into the potential future of our own Solar System.
The object in question is WD J1328−1450, a white dwarf located approximately 1,600 light-years from Earth. White dwarfs represent the dense, extinguished cores left behind after stars like the Sun exhaust their fuel and shed their outer layers. While this expansion often engulfs nearby planets, rocky bodies at greater distances can survive. These remnants may eventually break apart to form debris disks around the stellar corpse.
Until now, all observed gas disks around white dwarfs appeared as single, flat, rotating structures. Previous studies of 21 similar cases consistently showed a signal with two peaks. However, observations conducted between 2021 and 2023 using the X-shooter instrument on the European Southern Observatory's Very Large Telescope in Chile revealed a distinct four-peak signal. This signature confirms the presence of two concentric rings separated by a gap.
The dimensions of this system are significant relative to Earth-Moon distances. The inner ring extends from roughly 100,000 to 240,000 kilometers from the star, placing it closer than the Moon is to Earth. The outer ring begins at approximately 375,000 kilometers and stretches beyond 1.3 million kilometers. Repeated observations over more than two years indicate that this complex structure has remained stable.
Spectral analysis shows the gas contains calcium, oxygen, magnesium, and iron, a composition similar to rocks in our Solar System. Notably, the rings differ chemically: the inner ring is rich in magnesium, while the outer ring contains significantly less. This discrepancy suggests the debris originated from two bodies formed under different conditions or from distinct layers of a single object.
Researchers hypothesize that two surviving planetary bodies act as "guardians" maintaining this orderly structure by orbiting within their respective rings and releasing gas as they move through dust. Although these bodies cannot be seen directly, models suggest the inner one is asteroid-sized, while the outer one could be as large as Pluto or the Moon.
Nicola Pietro Gentile Fusillo, the study's lead author from the University of Trieste and INAF-Astronomical Observatory of Trieste, noted that while the planets are invisible, their presence is deduced from the gas composition and shape. He described the process as reconstructing the architecture of a destroyed planetary system from its final fragments, marking the first observation of such a complex configuration surviving around a dead star.
This discovery challenges current theories regarding the formation and evolution of these disks and the origin of their gas. It also has implications for Earth's future, as the Sun is expected to become a white dwarf in about five billion years, a process that could destroy our planet. Systems like WD J1328−1450 demonstrate that planetary remnants can persist in surprisingly organized forms even after their host star's death.
Sources: Focus.it.