[연구필요성]
Although most stars are born with multiple stars, the process of their formation is still a subject of debate. Therefore, finding out the formation mechanism of multiplicity is very important for a comprehensive understanding of star formation theory. So far, several scenarios have been proposed for the mechanism of multiplicity formation, but consensus has not yet been reached. In order to understand the multistar formation process, it is necessary to directly observe the moment when multiple stars are born with a high-resolution and high-sensitivity observation facility such as ALMA. In addition, in recent fetal star observations, “streamers”, which are gas structures flowing toward the fetal star, are often reported. Studying streamers is important because it shows how embryostars inhale gas to grow, but how these gaseous structures are formed is not yet fully understood. However, because the gas flow around a embryonic star in a multi-star system will have a complex structure, ALMA’s high-resolution imaging could be a powerful tool in studying streamer origins.
[연구성과/기대효과]
Through a study comparing high-resolution and high-sensitivity ALMA observations with hydrodynamic numerical simulations using supercomputers, this is the first case to show that the formation of a multi-star system is not the previously proposed binary mechanism, but a hybrid method in which the two mechanisms are combined. , suggested for the first time that spiral arm-shaped streamers that supply material to embryonic stars can be formed in the multiplicity formation process.
[본문]
An international research team led by Professor Jeongeun Lee of Seoul National University observed the multiple protostar system IRAS 04239+2436, where three embryonic stars are being born together, with the Atacama Large Millimeter/Submillimetre Interferometer (ALMA), and found three large spiral arms around the embryonic stars. discovered that it exists. These spiral arms are revealed in the light emitted by sulfur monoxide (SO) molecules. The gas distribution and velocity distribution obtained from the ALMA observations were compared with numerical simulations conducted by Professor Tomoaki Matsumoto of Hosei University using the Super Computer, and the streamer ( streamer), that is, it was confirmed that it plays the same role as an umbilical cord that supplies nutrients to the fetus. The origin of streamers, which have recently begun to be discovered, has been questioned, but the combination of ALMA observations and fluid dynamics simulations revealed for the first time that streamers can be created in the dynamic process of multiplicity formation.
The research team used ALMA to observe radio waves emitted by several molecules, including molecules of sulfur monoxide (SO) around the young multiprotostar system IRAS 04239+2436. IRAS 04239+2436 is a ‘triple protostellar system’, or triplets fetal star, located about 460 light-years from Earth. The research team expected that if they detected SO molecules in the region where the shock wave exists, they would be able to see the violent gas motion occurring around the embryonic star. As a result of observation, the research team detected SO molecules around the triplets and found that the distribution of SO molecules formed a large spiral arm extending up to 400 astronomical units. Also, by using the Doppler effect, they succeeded in obtaining the velocity distribution of a gas containing SO molecules.
Analysis of the gas’s motion revealed that the spiral arms tracked by the SO molecules were actually streamers flowing toward the triplet star. “The most shocking feature of this ALMA image is the large multi-armed structure distributed along the SO emission,” said Prof. Jeongeun Lee, emphasizing the significance of the discovery. “When I first saw this image, I had the impression that the structures were dancing, rotating together around the central fetal star. Later, it was revealed that these spiral arms are the channels that supply material to the fetal star.”
To investigate the motion of the gas in more detail, the research team compared the velocity of the gas obtained from the ALMA observations with that obtained from numerical hydrodynamic simulations reproducing multistar formation in interstellar gas clouds. The simulations, performed using ATERUI and ATERUI II, supercomputers dedicated to astronomy at the Computational Astrophysical Center of the National Astronomical Observatory (NAOJ) in Japan, show the gas perturbed around three fetal stars. produced shockwaves in the shape of spiral arms. Professor Matsumoto, who led the numerical simulation, said, “We found that gas flows in the shape of spiral arms towards the three embryo stars, which shows that the spiral arms act as streamers supplying gas to the embryo stars. In the simulation and observation, Since the velocity distributions of the obtained gases are consistent, it can be considered that the results of the numerical simulations well explain the origin of the streamer.” said.
The research team compared observational data and numerical simulations to study the birth mechanism of these triplets. So far, two scenarios have been proposed for multiplicity formation. The first is the ‘turbulent divergence scenario’, in which an interstellar cloud containing turbulence differentiates into several dense gas masses, and each of the masses evolves into a protostar. The second is a ‘disk eruption scenario’ in which a gas disk surrounding a protostar differentiates to form several stars through the process of creating a new protostar. Similar to the “turbulent eruption scenario”, the star formation process begins in the triplet fetus observed through this study, and then, like the “disk eruption scenario”, new star seeds are created in the disk, and the surrounding It can be described as a hybrid scenario in which a spiral arm connected to the turbulent flow of the gas is formed to inhale the material. Observation results and fluid dynamics simulation results are very similar, and this is the first time that multiplicity is formed by a hybrid scenario through the observed triplets. “This is the first time that the origins of a embryonic star and a streamer have been comprehensively revealed at the same time,” said Professor Matsumoto. “The combination of ALMA observations and simulations is a powerful tool for unlocking the secrets of star formation.”
Professor Jeongeun Lee said that from this study, it is possible to estimate how difficult it is to form a planet in a multi-star system. “Planets are formed in the disks of gas and dust that form around protostars. In this triplet system, the disk around the protostar is small, which means that the protostars are concentrated within a narrow central region, and that the protostars orbit close together. “Planets can only form after a long period of calm. So the surroundings of IRAS 04239 + 2436 are not conducive to planet formation.” Professor Matsumoto said, “The actual observation of the formation process of multiple star systems in the manner of a hybrid scenario will greatly contribute to resolving the controversy over multiple star formation scenarios. In addition, this study confirms the existence of the recently discovered streamer. Not only that, but we’ve made important strides by explaining how they form.”
The findings were published in the Astrophysical Journal on August 4, 2023.
