Fast gas flowing from young star caused by vaporization of the icy comet

A unique stage in the evolution of the planetary system has been imaged by astronomers, showing rapidly moving carbon monoxide flowing from a star system more than 400 light years away, a discovery that offers an opportunity to study the development of our own solar system.

Astronomers have detected rapidly moving carbon monoxide flowing from a young low-mass star: a unique stage in the evolution of the planetary system that may provide insight into how our own solar system evolved and suggests that the way systems develop may be more complicated than previously thought.

While it’s not clear how the gas is ejected so quickly, the team of researchers, led by the University of Cambridge, believe it could be produced from icy comets vaporized in the asteroid belt of the star. The results will be presented at the Five Years After HL Tau virtual conference in December.

The detection was made with the Large Millimeter / submillimeter Array (ALMA) from Atacama, Chile, as part of a survey of young “class III” stars, reported in an earlier article. Some of these Class III stars are surrounded by discs of debris, believed to be formed by the ongoing collisions of comets, asteroids and other solid objects, known as planetesimals, within the confines of recently formed planetary systems. The dust and debris left over from these collisions absorb light from their central stars and re-emit that energy in the form of a faint glow that can be studied with ALMA.

In the internal regions of planetary systems, the processes of formation of the planets are expected to result in the loss of all the hottest dust, and Class IIII stars are the ones that remain with – at most – dust. cold and dark. These weak belts of cold dust are similar to the known debris disks seen around other stars, similar to the Kuiper Belt in our own solar system, which is known to host much larger asteroids and comets.

In the investigation, the star in question, “ NO Lup, ” which makes up about 70% of our sun’s mass, was found to have a weak, low-mass dusty disk, but it was the only one Class III star where carbon monoxide has been detected, a first for this type of young star with ALMA. Although many young stars are known to still harbor the gas-rich planet-forming discs they were born with, NO Lup is more evolved and one would have expected it to have lost this primordial gas. after the formation of its planets.

Although the detection of carbon monoxide gas is rare, what made the sighting unique was the scale and speed of the gas, which prompted a follow-up study to explore its movement and origins.

“The simple detection of carbon monoxide gas was exciting, as no other young star of this type had been imaged before by ALMA,” said first author Joshua Lovell, a Ph.D. student at the Institute of Cambridge astronomy. “But when we took a closer look, we found something even more unusual: Given the distance between the gas and the star, it was moving much faster than expected. This left us in awe for a while. time.”

Grant Kennedy, a Royal Society University research associate at the University of Warwick, who led the study’s modeling work, found a solution to the puzzle. “We found a simple way to explain it: by modeling a ring of gas, but giving the gas an extra kick outward,” he said. “Other models have been used to explain young discs with similar mechanisms, but this disc is more like a disc of debris where we have never seen winds before. Our model has shown that the gas is quite consistent with a scenario where it is launched out of the system at around 22 kilometers per second, which is much higher than any stable orbital speed. “

Further analysis also showed that gas can be produced during collisions between asteroids, or during periods of sublimation – the change from a solid phase to a gas phase – on the surface of the star’s comets, believed to be rich in carbon monoxide.

There was recent evidence of this same process in our own solar system from NASA’s New Horizons mission, when it observed the Kuiper Belt object Ultima Thule in 2019 and found a sublimation evolution at the surface of the comet, which occurred about 4.5 billion years ago. The same event that vaporized comets in our own solar system billions of years ago may therefore have been first captured more than 400 light years away, in a process that may be common around stars forming planets, and have implications for how all comets, asteroids, and planets evolve.

“This fascinating star sheds light on the types of physical processes that shape planetary systems soon after they are born, right after they emerge from their protoplanetary disc,” said co-author Prof Mark Wyatt, also of the Institute of Astronomy. “While we have seen gas produced by planetesimals in older systems, the shear rate at which gas is produced in this system and its output nature are quite remarkable, and indicate a phase in the evolution of the system. planetary plan that we are seeing here for the first time. “

While the riddle is not fully resolved and more detailed modeling will be needed to understand how gas is ejected so quickly, what is certain is that this system is set to be the target of follow-up action. more intense.

“We hope that ALMA will be back online next year, and we will be arguing this system again in more detail,” Lovell said. “Given all that we have learned about this first step in the evolution of the planetary system with just a short 30 minute observation, there is still so much more this system can tell us.”

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