These debris disks often show sharply defined rings or spiral patterns, features that could signal the presence of orbiting planets. Astronomers study the disk features as a way to better understand the physical properties of known planets and possibly uncover new ones.
This chart compares the gas mass for several debris disk systems and shows where the photoelectric instability is most important. Systems like TW Hydrae contain so much gas that the instability is suppressed, but it could arise in relatively gas-free regions near the center of the disk.
Image Credit: NASA's Goddard Space Flight Center
But a new study by NASA scientists sounds a cautionary note in interpreting rings and spiral arms as signposts for new planets. Thanks to interactions between gas and dust, a debris disk may, under the right conditions, produce narrow rings on its own, no planets needed.
"When the mass of gas is roughly equal to the mass of dust, the two interact in a way that leads to clumping in the dust and the formation of patterns," said lead researcher Wladimir Lyra, a Sagan Fellow at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "In essence, the gas shepherds the dust into the kinds of structures we would expect to be see if a planet were present."
A paper describing the findings was published in the July 11 issue of Nature.
The warm dust in debris disks is easy to detect at infrared wavelengths, but estimating the gas content of disks is a much greater challenge. As a result, theoretical studies tend to focus on the role of dust and ice particles, paying relatively little attention to the gas component. Yet icy grains evaporate and collisions produce both gas and dust, so at some level all debris disks must contain some amount of gas.
"All we need to produce narrow rings and other structures in our models of debris disks is a bit of gas, too little for us to detect today in most actual systems," said co-author Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md.
Here's how it works. When high-energy ultraviolet light from the central star strikes a clump of dust and ice grains, it drives electrons off the particles. These high-speed electrons then collide with and heat nearby gas.
The rising gas pressure changes the drag force on the orbiting dust, causing the clump to grow and better heat the gas. This interaction, which the astronomers refer to as the photoelectric instability, continues to cascade. Clumps grow into arcs, rings, and oval features in tens of thousands of years, a relatively short time compared to other forces at work in a young solar system.
A model developed by Lyra and Kuchner shows the process at work.
"We were fascinated to watch this structure form in the simulations," Lyra said. "Some of the rings begin to oscillate, and at any moment they have the offset appearance of dust rings we see around many stars, such as Fomalhaut."
In addition, dense clumps with many times the dust density elsewhere in the disk also form during the simulation. When a clump in a ring grows too dense, the ring breaks into arcs and the arcs gradually shrink until only a single compact clump remains. In actual debris disks, some of these dense clumps could reflect enough light to be directly observable.
"We would detect these clumps as bright moving sources of light, which is just what we're looking for when we search for planets," adds Kuchner.
The researchers conclude that the photoelectric instability provides a simple and plausible explanation for many of the features found in debris disks, making the job of planet-hunting astronomers just a little bit harder.Francis Reddy
Francis Reddy | EurekAlert!
NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center
Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
17.11.2017 | Physics and Astronomy
17.11.2017 | Health and Medicine
17.11.2017 | Studies and Analyses