Fast-Moving Gas Near Distant Star May Be Caused by Vaporizing Icy Comets

Astronomers have detected fast-moving carbon monoxide gas flowing away from a young, low-mass star, the No Lup system, a University of Cambridge press statement reveals.

This, the researchers say, constitutes a unique observation into a stage of planetary system evolution that may help us to understand how our own solar system came into existence.

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A first for Class III stars

Although it is still unclear why the gas is flowing so quickly away from the No Lup system, the team of researchers, led by the University of Cambridge, believe the gas might be produced from icy comets that are being vaporized in the star’s asteroid belt.

The researchers will have their findings published in the Monthly Notices of the Royal Astronomical Society and will also present them at the Five Years After HL Tau virtual conference.

The observation was made using the Atacama Large Millimetre/submillimetre Array (ALMA) in Chile, as part of a survey of young ‘class III’ stars.

Some of these class III stars are surrounded by debris discs, which are believed to have been formed by repeated collisions of comets and asteroids in the outer reaches of recently formed planetary systems.

The dust and debris from these collisions absorb light from the system's stars a re-radiates it as a faint glow that can be studied with ALMA.

In the researchers' survey, the star 'NO Lup', which is about 70 percent the mass of our sun, was found to have a faint, low-mass dusty disc. It was the only class III star where carbon monoxide gas was detected, a first for this type of young star in ALMA observations.

While the detection of carbon monoxide gas is rare, the real surprise in the 'NO' Lup' observation was the scale and speed of the gas, which prompted a follow-up study.

Gas moving with perplexing speed

"Just detecting carbon monoxide gas was exciting, since no other young stars of this type had been previously imaged by ALMA," said first author Joshua Lovell, a Ph.D. student from Cambridge’s Institute of Astronomy.

"But when we looked closer, we found something even more unusual: given how far away the gas was from the star, it was moving much faster than expected. This had us puzzled for quite some time," he continued.

Grant Kennedy, Royal Society University Research Fellow at the University of Warwick, who led the modeling work on the study, came up with a solution to the mystery.

"We found a simple way to explain it: by modeling a gas ring, but giving the gas an extra kick outward," Kennedy explained. "Our model showed the gas is entirely consistent with a scenario in which it’s being launched out of the system at around 22 kilometers per second, which is much higher than any stable orbital speed."

Further analysis showed that the gas might also be produced during collisions between asteroids. 

"This fascinating star is shedding light on what kind of physical processes are shaping planetary systems shortly after they are born, just after they have emerged from being enshrouded by their protoplanetary disk," said co-author Professor Mark Wyatt, also from the Institute of Astronomy.

"While we have seen gas produced by planetesimals in older systems, the shear rate at which gas is being produced in this system and its outflowing nature is quite remarkable and point to a phase of planetary system evolution that we are witnessing here for the first time," he continued.

Though the mystery is yet to be fully solved, the researchers say they are keen to continue delving deeper with detailed modeling and measurements in a bid to gain a further understanding of planetary formation.