Dust rings may not always be 'calling cards of unseen planets'
London: Contrary to popular belief that sharp rings of dust around stars are always carved by planets, a new study has suggested that the rings can even form on their own.
It certainly may be a bad news for those who use the structures to direct them to stars that host planets.
The discovery also has implications for the existence of a contentious candidate exoplanet.
The discs of dust and gas debris surrounding stars occasionally produce sharply defined or elongated rings. These were believed to be the calling cards of unseen planets, carved by the bodies as they travel through the disc.
“I call it the dark matter argument,” the New Scientist quoted Wladimir Lyra at NASA’s Jet Propulsion Laboratory in Pasadena, California, as saying.
“There is something you are seeing that you cannot explain, and you blame the gravity of something you cannot see.”
Now Lyra and Marc Kuchner at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland, have demonstrated that interactions between dust and gas alone can account for the rings.
Dust concentrates in regions of high-pressure gas. As the star heats the dust, it in turn causes the gas to heat up and expand, creating higher pressure which then accumulates more dust.
Lyra and Kuchner replicated this feedback process and, with no planets in their model, they created numerous types of structure, including elongated rings and clumps.
As far as the controversial planet is concerned, the work indicates that a bright dot in the disc around the star dubbed Fomalhaut may not be a planet.
In 2004, the Hubble Space Telescope observed the dot inside a gap in the dusty disc around Fomalhaut. Few astronomers assumed that the dot was a giant planet that had carved out the gap. That would have made the object, dubbed Fomalhaut b, one of only a few exoplanets to be imaged directly.
But follow-up observations did not detect the object at infrared wavelengths, implying the dot was not a Jupiter-like planet, whose infrared glow should have been observed.
Instead, some ventured that the dot was a dust cloud created by colliding asteroids and that one or more planets too small to be spotted might have carved the dusty disc’s sharp edges.
Markus Janson of Princeton University in New Jersey, who has studied the Fomalhaut system, insists that it is still too soon to tell what the bright dot is and why the close by dust ring appears so sculpted.
But he is manoeuvred that these structures can form because of the hydrodynamics of dust and gas alone:
“I’m now more open to the idea that maybe there are no planets [around Fomalhaut] at all,” Janson added.