Astronomers using the Atacama Large Millimeter Array (ALMA) have detected very low levels of carbon monoxide gas in the debris disk around the nearby star HD 181327, in amounts that are consistent with the comets in our own Solar System.
Illustration of the debris disk surrounding the Sun-like star HD 181327. Image credit: Amanda Smith / University of Cambridge.
HD 181327, also known as TYC 8765-638-1 and WISE J192258.97-543217.8, is a young F5/6 main sequence star located approximately 169 light-years away in the constellation of Pictor.
It is about 23 million years old and has a mass about 30% greater than our Sun.
“Young systems such as this one are very active, with comets and asteroids slamming into each other and into planets,” said Sebastian Marino, an astronomer at the Institute of Astronomy at the University of Cambridge.
“The system has a similar ice composition to our own, so it’s a good one to study in order to learn what our Solar System looked like early in its existence.”
Using ALMA, Marino and co-authors observed HD 181327, which is surrounded by a ring of dust caused by the collisions of comets, asteroids and other bodies.
It’s likely that this star has planets in orbit around it, but they are impossible to detect using current telescopes.
“Assuming there are planets orbiting this star, they would likely have already formed, but the only way to see them would be through direct imaging, which at the moment can only be used for very large planets like Jupiter,” said Luca Matra, also an astronomer at the University of Cambridge’s Institute of Astronomy.
In order to detect the possible presence of comets, the team used ALMA to search for signatures of gas, since the same collisions which caused the dust ring to form should also cause the release of gas.
Until now, such gas has only been detected around a few stars, all substantially more massive than the Sun.
Using simulations to model the composition of the system, the astronomers were able to increase the signal to noise ratio in the ALMA data, and detect very low levels of carbon monoxide gas.
“This is the lowest gas concentration ever detected in a belt of asteroids and comets – we’re really pushing ALMA to its limits,” Marino said.
“The amount of gas we detected is analogous to a 200 km diameter ice ball, which is impressive considering how far away the star is,” Matra added.
The research has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.
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S. Marino et al. 2016. Exocometary gas in the HD 181327 debris ring. MNRAS, accepted for publication
