Astronomers using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) have discovered an unusual double ring of planetary debris around the white dwarf J1328−1450. The two rings are separated by an apparent gap that may be maintained by surviving planetary bodies, including one that could be as large as Pluto or the Moon. The system offers a possible preview of what may happen to planetary systems, including our own, after their stars die.
A dead star surrounded by two debris rings
White dwarfs are extremely dense remnants left behind when Sun-like stars run out of fuel. Before becoming white dwarfs, these stars expand dramatically and shed their outer layers, exposing their nuclei.
This transformation can have devastating consequences for nearby planets. An expanding star may engulf worlds in close orbits, while more distant rocky objects could survive the initial upheaval but later be torn apart by gravitational disturbances. Their remains can form a rotating disk around the stellar remnant.
Astronomers have observed debris disks around other white dwarfs, but J1328−1450 appears different. Rather than a single ring of vaporized planetary material, it is surrounded by two concentric rings: one closer to the star and one farther away. The rings remain distinctly separated, creating a structure scientists are still working to explain.
“It has been known for some time that planets can survive the deformation of their central star, but this is the first example of a complex system in which a double debris disk and two planetesimals could survive,” says Nicola Gentile Fusillo, an astronomer at Italy’s University of Trieste and lead author of the study published in 2006 in Nature Astronomy.
“The structure seen in this system is particularly interesting because the two gaseous rings are surprisingly stable and remain separated by a gap,” says co-author Felipe Lagos Vilchez, an astronomer at the University of Warwick in the UK and the Federico Santa Maria Polytechnic University in Chile.
“This system provides a rare glimpse into the violent and chaotic process by which planetary systems end, and suggests that dead stars may have much more complex disk structures than previously realized,” adds Gentile Fusillo, who is also affiliated with the INAF observatory in Trieste.
Surviving bodies may keep the rings apart
Researchers suspect that two surviving planetary bodies, each following its own orbit, may be responsible for maintaining the double-ring structure.
One object is associated with the inner ring and is thought to be comparable in size to a typical asteroid, which is only a few kilometers across. The other lies farther from the star and could be much larger, potentially reaching the size of Pluto or the Moon.
These objects are known as planetesimals, a term for small solid bodies involved in the formation and evolution of planetary systems. Although the suspected survivors have not been directly observed, their gravitational influence could explain why the debris remains arranged in two separate rings instead of spreading into a continuous disk.
Observations reveal a complex planetary remnant
The evidence comes from observations made with the X-Shooter instrument on ESO’s VLT in Chile’s Atacama Desert. X-Shooter analyzes light across a broad range of wavelengths, enabling astronomers to study the composition and motion of material around distant objects.
Previously discovered white-dwarf debris disks shared recognizable features consistent with single, flat, rotating disks. J1328−1450 breaks that pattern. Its observations revealed a distinctive signature from the double disk, indicating a more complex arrangement of planetary remnants.
Chemical clues from a destroyed world
The debris also contains clues about the world or worlds that once orbited the star. Astronomers detected calcium, oxygen, magnesium and iron—elements commonly found in rocky planetary material throughout the solar system. Their presence indicates that the rings contain solid planetary debris rather than only gas left over from the star itself.
The chemical compositions of the two rings are markedly different. The inner ring contains a large amount of magnesium gas, while the outer ring contains significantly less.
One possibility is that the material came from two separate planets with different compositions. If so, the system could preserve evidence of multiple destroyed worlds.
Another possibility is that both rings formed from different layers of the same planetary body. One ring might contain material from the body’s outer shell, while the other could include deeper material, such as its core.
Either explanation could help scientists understand how rocky worlds are destroyed and how complex structures can persist long after a star has exhausted its fuel.
A possible preview of the solar system’s future
In billions of years, the Sun is expected to undergo a similar evolution. It will expand into a red giant, shed its outer layers and eventually become a white dwarf. The inner solar system will change dramatically during this process, and Earth itself may be destroyed.
J1328−1450 suggests, however, that a star’s death does not necessarily erase its entire planetary system. Some objects may survive, while others may break apart into fragments that continue orbiting the stellar remnant in complex configurations.
By studying this distant white dwarf and its unusual double ring, astronomers have a rare opportunity to investigate what can remain after a planetary system undergoes such profound changes.
“This system therefore provides a surprising glimpse into what the future of planetary systems, including systems like ours, will look like,” concludes Lagos-Vilches.
Source: www.sciencedaily.com
