Astronomers have identified two distinct rings of planetary debris around a dying star, in a configuration never before observed in this type of system. The discovery could help understand what will happen to the planets of the Solar System when the Sun reaches the end of its evolution, in billions of years.
The star, a white dwarf named J1328−1450, is located about 1,600 light-years from Earth, in the constellation Virgo. It is the remnant core of a star that exhausted its fuel, expanded, and shed its outer layers.
Around it, researchers found two concentric rings of gas arising from planetary material, possibly held by rocky bodies that survived the star’s transformation.
According to scientists, the configuration is unusual because the 21 similar systems identified previously displayed only a single gaseous disk of debris, and not two separate rings.
The study was published in the scientific journal Nature Astronomy, based on observations conducted by the Very Large Telescope (VLT) of the European Southern Observatory, located in Chile.
What makes the two rings so unusual?
The white dwarf J1328−1450 contains about 47% of the Sun’s mass within a diameter comparable to Earth’s, a characteristic that highlights the enormous density of these stellar remnants.
Researchers believe that the two rings may have been shaped by planetary bodies or smaller rocky objects that survived the star’s final stages of evolution.
One of these bodies could be roughly Pluto-sized, while the other would be smaller. The objects, however, were not observed directly: their possible existence is a proposed explanation for the rings’ structure.
“This shows that the remnants of a planetary system can have a structure far more complex than we previously thought and further reinforces the idea that rocky planetary bodies can survive the transformation of a star into a white dwarf,” said astronomer Felipe Lagos-Vilches of the Federico Santa María Technical University in Chile, one of the study’s authors.
The scientists also identified differences in the chemical composition of the two rings, which may help explain the debris’s origin.
“The outer ring shows a strong depletion of magnesium compared with the inner ring. This suggests that they may have originated from different parent bodies or, possibly, from different layers of a rocky body that was disrupted as it approached too close to the white dwarf due to its strong gravitational field,” explained Lagos-Vilches.
How can planets survive the death of a star?
According to the researchers, the star that gave rise to J1328−1450 may have hosted a planetary system before it transformed into a red giant.
During this phase, the star dramatically increases in size and may swallow the closer planets. Bodies orbiting at greater distances, however, have a greater chance of surviving.
“The planetary system did not disappear completely. Some surviving rocky bodies may have been gravitationally perturbed into highly eccentric orbits that brought them close to the white dwarf,” said Lagos-Vilches.
These orbital changes could drive the surviving objects to regions where the intense gravitational force of the white dwarf causes their fragmentation.
“The objects that came close enough were torn apart by the white dwarf’s gravitational force. Their material spread out forming a debris disk containing dust and gas. However, two relatively large rocky bodies may have survived within these debris,” explained the astronomer.
The presence of these two objects could help explain why the material around the star is distributed into two separate gaseous rings, instead of forming a single disk.
The discovery also offers clues about a possible future for the Solar System.
In about 5 billion years, the Sun is expected to exhaust the fuel in its core and enter the red-giant phase, expanding considerably.
Thereafter, it will shed its outer layers and leave behind an extremely dense core: a white dwarf.
This transformation should profoundly alter the Solar System, with different consequences for each planet.
“Mercury and Venus are expected to be swallowed by the expanding Sun, while there is not yet a clear consensus on whether Earth will also be engulfed during this phase,” said Lagos-Vilches.
“The fate of the outer planets is different. Jupiter, Saturn, and more distant bodies should have a much greater chance of surviving.”
Even after the Sun becomes a white dwarf, the Solar System may continue to undergo major changes.
Remaining planets, moons and asteroids may have their orbits altered and end up approaching the stellar core. If they get close enough, they could be torn apart by gravitational forces, forming debris disks similar to those identified around J1328−1450.
“A debris disk like the one around J1328−1450 could, therefore, represent a possible stage in the very distant future of our own planetary system,” concluded Lagos-Vilches.
