Fast-moving gas flowing away from the young star caused by the vaporization of an icy comet

Astronomers have captured a unique stage in the evolution of the planetary system, showing fast-moving carbon monoxide gas flowing out of a star system over 400 light-years away, a discovery that offers the opportunity to study how our solar system has developed.

Astronomers have detected fast-moving carbon monoxide gas flowing away from a young, low-mass star – a unique stage in the evolution of the planetary system that can provide insight into how our solar system has evolved and suggests that the way where systems are developed could be more complicated than previously thought.

While it’s unclear how the gas is ejected so quickly, the team of researchers, led by the University of Cambridge, believe it may be produced by vaporized icy comets in the star’s asteroid belt. The results will be presented at the Five Years After HL Tau virtual conference in December.

The detection was carried out with the Atacama Large Millimeter / submillimetre Array (ALMA) in Chile, as part of a survey of “class III” young stars reported in a previous paper. Some of these Class III stars are surrounded by debris disks, which are believed to be formed by the continuous collisions of comets, asteroids and other solid objects, known as planetesimals, in the outermost reaches of newly formed planetary systems. The residual dust and debris from these collisions absorb light from their central stars and radiate that energy again as a faint glow that can be studied with ALMA.

In the inner regions of planetary systems, planet-forming processes should result in the loss of all the hottest dust, and class IIII stars are the ones that are left with – at most – cold, faint dust. These faint cold dust belts are similar to the known debris discs seen around other stars, similar to the Kuiper belt in our solar system, which is known to host much larger asteroids and comets.

In the survey, the star in question, ‘NO Lup’, which is about 70% of the mass of our sun, was found to have a faint, low-mass dusty disk, but it was the only Class III star in which the Carbon monoxide gas was detected a first for this type of young star with ALMA. Although many young stars are known to still harbor the forming disks of the gas-rich planets they were born with, NO Lup is more evolved and could have been expected to have lost this primordial gas after its planets formed.

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

“The detection of carbon monoxide gas alone was exciting, since no other young star of its kind had previously been captured by ALMA,” said first author Joshua Lovell, a doctoral student at the Institute of Astronomy of Cambridge. “But when we looked closer, we found something even more unusual: given how far the gas was from the star, it was moving much faster than expected. This puzzled us for quite some time.”

Grant Kennedy, a researcher with the Royal Society University at the University of Warwick who led the study’s modeling work, found a solution to the puzzle. “We found an easy way to explain it: by modeling a gas stove, 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 debris disc in which we have never seen winds before. Our model showed that the gas is entirely consistent with one. scenario where it is launched out of the system at about 22 kilometers per second, which is much higher than any stable orbital velocity. ”

Further analysis also showed that gas can be produced during asteroid collisions, or during periods of sublimation – the transition from a solid to a gas phase – on the surface of the star’s comets, which are supposed to be rich in carbon monoxide.

There has been recent evidence of this same process in our solar system since NASA’s New Horizons mission, when it observed the Kuiper belt object Ultima Thule in 2019 and found the evolution of sublimation on the comet’s surface, which occurred around 4 , 5 billion years ago. The same event that vaporized comets in our solar system billions of years ago may therefore have been first captured over 400 light-years away, in a process that may be common around planet-forming stars and have implications. about how all comets, asteroids and planets evolve.

“This fascinating star is shedding light on the kind of physical processes that are shaping planetary systems soon after their birth, right after they emerged from being enveloped by their protoplanetary disk,” said co-author Mark Wyatt, also of the Institute of Astronomy. “Although we have seen the gas produced by planetesimals in older systems, the shear rate at which the gas is produced in this system and its outgoing nature are quite remarkable and indicate a phase of evolution of the planetary system that we are witnessing. here for the first time. “

Although the puzzle is not completely solved and further detailed modeling will be required to understand how the gas is expelled so quickly, what is certain is that this system is set to be the target of more intense follow-up measurements.

“We hope ALMA comes back online next year and we will make the case to look at this system again in greater detail,” Lovell said. “Given what we have learned about this early stage in the evolution of the planetary system with only a brief 30 minute observation, there is still a lot more that this system can tell us.”

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