Dust discs of nearby red dwarfs could reveal planetary secrets

Australian National University / University of New South Wales Press Release

16 September 2015 Astronomy Now

Artist’s depiction of a dusty ‘circumstellar’ disc orbiting a young red dwarf star. Illustration credit: NASA/JPL-Caltech/T. Pyle (SSC).
Artist’s depiction of a dusty ‘circumstellar’ disc orbiting a young red dwarf star. Illustration credit: NASA/JPL-Caltech/T. Pyle (SSC).
An accidental find of a collection of young red dwarf stars close to our solar system could give us a rare glimpse of slow-motion planet formation. Astronomers from The Australian National University (ANU) and University of New South Wales (UNSW), Canberra found large discs of dust around two of the stars, telltale signs of planets in the process of forming.

“We think the Earth and all the other planets formed from discs like these so it is fascinating to see a potential new solar system evolving,” said the lead researcher Dr. Simon Murphy, from the ANU Research School of Astronomy and Astrophysics.

“However, other stars of this age usually don’t have discs any more. The red dwarf discs seem to live longer than those of hotter stars like the Sun. We don’t understand why,” said Dr. Murphy.

Artist’s conception of an exoplanet orbiting a cool red dwarf star like TWA 35/36 in the study. Illustration credit: David A. Aguilar (CfA/Harvard-Smithsonian).
Artist’s conception of an exoplanet orbiting a cool red dwarf star like TWA 35/36 in the study. Illustration credit: David A. Aguilar (CfA/Harvard-Smithsonian).
The discovery of objects like these two challenges current theories about planet formation, said co-author Professor Warrick Lawson from UNSW Canberra. “It suggests the planet forming process can endure a lot longer than previously thought,” he said.

The red dwarfs may also host planets that have already formed from the dusty discs, Dr. Murphy added. “I think a lot of telescopes will be turned toward them in the next few years to look for planets,” he said.

The giveaway that the red dwarfs had discs around them was an unusual glow in the infrared spectrum of the stars.

Although the discs were not observed directly, Dr. Murphy said such close red dwarfs offered a good chance of catching a rare direct glimpse of a disc, or even a planet, by employing specialised telescopes. “Because they are fainter than other stars and there is not as much glare, young red dwarfs are ideal places to directly pick out recently formed planets,” he said.

The location of one of the red dwarfs, called 2M1239-5702, is near Gacrux — a red giant star at the top of the Southern Cross. Image credit: Akira Fujii.
The location of one of the red dwarfs, called 2M1239-5702, is near Gacrux — a red giant star at the top of the Southern Cross. Image credit: Akira Fujii.
Professor Lawson said the ability to detect these dim stars has improved dramatically in recent decades, revealing a wealth of information. “Less than 20 years ago, the notion that the nearest part of the galaxy would be littered with young stars was a completely novel one,” he said.

“Most of these objects lie in the southern sky and thus are best accessed by telescopes in the Southern Hemisphere, including those operated by ANU and Australia more broadly,” added Professor Lawson.

The research is published in the Monthly Notices of the Royal Astronomical Society.

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