On October 6th, an international research team led by Specially Appointed Assistant Professor Satoshi Ohashi of the National Astronomical Observatory of Japan, in which Assistant Professor Aya Higuchi (Faculty of Science and Engineering, Department of Science and Engineering, Physics Course) of Tokyo Denki University (President: Tadahiko Ibamoto) is participating, We announced our research results titled “The first step in planet formation has been captured.”
*This project is supported by Interuniversity Research Institute Corporation National Institutes of Natural Sciences, National Astronomical Observatory of Japan, National University Corporation Ibaraki University, and Educational Corporation
This is a joint announcement by Tokyo Denki University and Tokyo Institute of Technology.
*For details on the research, please see below.
Research overview
An international research team led by Specially Appointed Assistant Professor Satoshi Ohashi of the National Astronomical Observatory of Japan conducted high-resolution observations and multi-wavelength observations using ALMA of the protoplanetary disk around the relatively young protostar DG Taurus, and discovered the disk’s size. We investigated in detail the structure and the size and amount of dust that is the material of planets. As a result, the disk was flat and there were no traces of planets, indicating that it appeared on the eve of planet formation. Furthermore, it was found that the dust was growing larger on the outside, and that the concentration of dust was higher than usual on the inside. We have clarified the first step in how planet formation begins.
Research details
Figure 1 Radio intensity map at a wavelength of 1.3 mm of the disk around DG Taurus star observed with ALMA. Unlike the disks surrounding older protostars, no ring-like structures have formed, suggesting that they are just before planet formation.
Credit: ALMA (ESO/NAOJ/NRAO), S. Ohashi et al.
Unraveling the mystery of how planets like Earth were created is an important issue in understanding the origin of life. It is believed that planets are formed by gathering interstellar dust and interstellar gas in a protoplanetary disk surrounding a protostar, but it is unclear when, where, and how planet formation begins. The first step is unknown. On the other hand, it is known that when a planet is formed inside a disk, its gravity creates a ring-like pattern on the disk. In fact, ALMA observations have found ring structures in many protoplanetary disks, suggesting the existence of planets. However, in order to investigate the process by which planets are formed, it is important to closely examine disks that are certain to contain no planets yet. However, due to the difficulty of discovering disks without traces of planets and the difficulty of examining such disks in detail, it is still unclear how planet formation begins. yeah.
Therefore, an international research group focused on DG Taurus, a relatively young object among protostars, and used ALMA to examine the disk surrounding the protostar in detail. We observed the distribution of radio wave intensity at a wavelength of 1.3 mm emitted by dust within the disk at an extremely high spatial resolution of 0.04 arcsec, and revealed the detailed structure of the disk. The results revealed that the disk around DG Tauri star is flat and lacks the ring-like pattern seen in disks around relatively old protostars. This is because there are no planets yet in the disk of DG Taurus, and it is thought that this image was captured on the eve of planet formation.
Figure 2 (Top) Radio intensity maps of the DG Taurus star disk observed with ALMA at wavelengths of 0.87 mm, 1.3 mm, and 3.1 mm, and polarization intensity maps of radio waves scattered by dust at wavelengths of 0.87 mm and 3.1 mm. (Bottom) Observation simulation that best matches the observation results above.
Credit: ALMA (ESO/NAOJ/NRAO), S. Ohashi et al.
Furthermore, we observed the disk at different wavelengths (0.87 mm, 1.3 mm, 3.1 mm), and investigated the radio wave intensity and polarization intensity (the extent to which the vibration directions of the radio waves are aligned). Depending on the size and distribution pattern of dust, the ratio of radio wave intensities at different wavelengths and the polarization intensity of radio waves scattered by dust change. Therefore, by comparing observation results with observation simulations with various patterns of dust size and amount distribution and looking for patterns that closely match, we can determine how much interstellar dust, which is the material for planets, is growing. It is possible to estimate the distribution of its size and amount. Therefore, the size of the dust is relatively larger on the outer side of the disk (approximately 40 astronomical units and beyond; a little farther than the distance equivalent to Neptune in the solar system) than on the inner side, which means that the process of planet formation is progressing. I understand that. Previous theories of planet formation have believed that planet formation begins from the inside, but this result contradicts that prediction and suggests that planet formation may actually start from the outside. On the other hand, although the size of the dust is small in the inner space, the content of dust relative to gas is about 10 times higher than in normal interstellar space. Furthermore, these dust particles are often deposited on the disk surface, suggesting that this is the stage in which the planet-forming materials are stored. In the future, it is possible that this accumulation of dust will trigger planet formation.
This observation was made possible by ALMA’s extremely high spatial resolution of 0.04 arc seconds, as well as the observation of radio waves emitted by the dust that contain polarized light at three wavelengths. This research is the first in the world to reveal the size and amount of dust in a flat disk with no traces of planets. As a result, new aspects of planet formation sites have been revealed that could not be expected from previous theoretical research or observations of disks where traces of planet formation can be seen. Commenting on the significance of this research, Specially Appointed Assistant Professor Satoshi Ohashi of the National Astronomical Observatory of Japan said, “Up until now, ALMA has succeeded in capturing a variety of disk structures and revealed the existence of planets. To answer the question “How does planet formation begin?”, it is important to observe flat disks with no traces of planet formation.This research has clarified the initial conditions for planet formation. I think this is a very important achievement.”
This research result was published in the American academic journal The Astrophysical Journal in August 2023 as “Dust Enrichment and Grain Growth in a Smooth Disk around the DG Tau Protostar Revealed by ALMA Triple Bands Frequency Observations” by Satoshi Ohashi et al. Published on the 28th (DOI: 10.3847/1538-4357/ace9b9.)
This research was supported by the Japan Society for the Promotion of Science Grant-in-Aid for Scientific Research (JP18H05441, JP19K23469, JP20K04017, JP20K14533, JP20H00182, JP22H01275, JP23H01227), the RIKEN pioneering project, Evolution of Matter in the Universe, the DFG-Grant “INSIDE: The INner regions of protoplanetary disks:SImulations andD obsErvations” (project No. 465962023), the EC H2020 research and innovation program for the project “Astro-Chemical Origins” (ACO, No. 811312) and the PRIN-MUR 2020 MUR BEYOND-2p ( Astrochemistry beyond the second period elements, Prot. 2020AFB3FX).
The ALMA telescope (Atacama Large Millimeter/submillimeter Array: ALMA) is a project conducted by the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the Japanese National Institutes of Natural Sciences (NINS) in the Republic of Chile. It is an international astronomical observation facility operated in cooperation with Japan. The construction and operation costs of ALMA will be funded by ESO, NSF and its partners National Research Council of Canada (NRC), National Science and Technology Commission of Taiwan (NSTC), NINS and its partner Academia Sinica (Taiwan). AS) and the Korea Astronomy and Space Science Institute (KASI). Construction and operation of ALMA will be carried out by ESO on behalf of its member countries, the U.S. National Radio Astronomy Observatory managed by the Northeast Association of Universities (AUI) on behalf of North America, and the National Astronomical Observatory of Japan on behalf of East Asia. We will implement it. The purpose of the Joint ALMA Observatory (JAO) is to carry out unified execution and management of the construction, test observations, and operation of ALMA.
Presenting organization
National Astronomical Observatory of Japan, Ibaraki University, Tokyo Denki University, Tokyo Institute of Technology
Presenter
Satoshi Ohashi (Specially Appointed Assistant Professor, ALMA Project, National Astronomical Observatory of Japan)
Munetake Momose (Professor, Graduate School of Science and Engineering, Ibaraki University)
Aya Higuchi (Assistant Professor, Physics Course, Faculty of Science and Engineering, Tokyo Denki University)
Takashi Tsukagoshi (Associate Professor, Department of Systems Information, Faculty of Engineering, Ashikaga University)
Satoshi Okuzumi (Associate Professor, Department of Earth and Planetary Sciences, Tokyo Institute of Technology)
Hidekazu Tanaka (Professor, Department of Astronomy, Graduate School of Science, Tohoku University)
Contact information
○National Astronomical Observatory
・About the research content
Satoshi Ohashi Specially Appointed Assistant Professor, ALMA Project, National Astronomical Observatory of Japan
RIKEN Pioneering Research Headquarters Sakai Star and Planet Formation Laboratory Visiting Researcher
Phone: 080-6721-1097 (Available until October 13th) / Email: satoshi.ohashi@nao.ac.jp
・About reporting
Naoko Inoue, Specially Appointed Specialist, ALMA Project, National Astronomical Observatory of Japan
Phone: 0422-34-3630 / Email: naoko.inoue@nao.ac.jp
○Tokyo Denki University
・About the research content
Aya Higuchi Tokyo Denki University, Faculty of Science and Engineering, Department of Science and Engineering, Department of Science, Physics Course, Assistant Professor
Phone: 049-296-5347 / Email: aya.higuchi@mail.dendai.ac.jp
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