Astronomers using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) have discovered an unusual double debris disk around the white dwarf J1328−1450. The two separate rings of planetary material are divided by a gap that may be maintained by surviving planetary bodies, including one potentially as large as Pluto or the Moon. The system offers a rare view of what can remain after a planetary system undergoes the death of its star—and may provide clues about the distant future of our own solar system.
A complex disk around a dead star
The discovery differs from previously observed debris systems around white dwarfs. Rather than forming a single disk, the material around J1328−1450 appears to be arranged in two concentric rings, with one orbiting farther from the star than the other.
“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 the University of Trieste in Italy and lead author of the study published in 2006 in Nature Astronomy.
White dwarfs are the extremely dense remnants of Sun-like stars. When such a star exhausts its fuel, it expands dramatically, sheds its outer layers and leaves behind an exposed stellar core.
That transformation can destroy nearby planets. Worlds orbiting too close to the expanding star may be swallowed, while more distant rocky bodies can survive the initial expansion but later be disrupted by gravitational interactions. Their remains may then form a rotating disk around the white dwarf.
“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,” added Gentile Fuscillo, who is also affiliated with the INAF observatory in Trieste.
Possible surviving planetary bodies
Researchers suspect that two surviving planetary bodies, each following its own orbit, could be helping to preserve the gap between the rings.
One object appears to be associated with the inner ring and is thought to be comparable in size to a typical asteroid, measuring only a few kilometres across. The second object is farther from the star and could be much larger, potentially reaching the size of Pluto or the Moon.
These objects are known as planetesimals: small solid bodies involved in the formation and evolution of planetary systems. Although neither suspected survivor has been directly observed, its gravitational influence could explain why the debris remains separated into two rings instead of spreading into a single continuous disk.
The evidence comes from observations made with the X-Shooter instrument on ESO’s VLT in Chile’s Atacama Desert. X-Shooter examines light across a broad range of wavelengths, allowing astronomers to investigate the chemical composition and motion of material around distant objects.
Previously identified white-dwarf debris disks shared observational characteristics consistent with a single, flat, rotating disk. J1328−1450 does not fit that pattern. Its observations show a distinctive signature from a double disk, indicating a substantially more complex arrangement of planetary debris.
Chemical clues from a destroyed world
The debris also preserves information about the rocky body or bodies that once orbited the star. Astronomers detected calcium, oxygen, magnesium and iron—elements commonly found in rocky planetary material in our solar system. Their presence indicates that the rings contain solid planetary debris rather than material left over solely from the star.
The chemical compositions of the two rings are notably different. The inner ring contains a large amount of magnesium gas, while the outer ring contains significantly less.
One explanation is that the material came from 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 a single planetary body. One ring could contain material from the body’s outer shell, while the other could include deeper material, such as material from its core.
Either scenario could help scientists understand how rocky worlds are destroyed and how complex structures can persist long after their star has exhausted its fuel.
A possible glimpse of the Solar System’s future
In billions of years, the Sun will undergo a similar sequence of changes. It will expand into a red giant, shed its outer layers and eventually become a white dwarf. The inner Solar System will be radically altered during this process, and Earth itself may be destroyed.
Observations of J1328−1450 suggest, 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 arrangements.
By studying this distant white dwarf and its unusual double ring, astronomers can investigate what remains after a planetary system experiences such a dramatic transformation.
“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