The formation of protoplanetary discs during the collapse of molecular dense cores is significantly influenced by angular momentum transport, notably by the magnetic torque. In turn, the evolution of the magnetic field is determined by dynamical processes and non-ideal MHD effects such as ambipolar diffusion. Considering simple relations between various timescales characteristic of the magnetized collapse, we derive an expression for the early disc radius, $ r \simeq 18 \, {\rm AU} \, \left({η_{\rm AD} / 0.1 \, {\rm s}} \right)^{2/9} \left({B_z / 0.1\, {\rm G}} \right) ^{-4/9} \left({M / 0.1 \msol} \right) ^{1/3},$ where $M$ is the total disc plus protostar mass, $η_\mathrm{AD}$ is the ambipolar diffusion coefficient and $B_z$ is the magnetic field in the inner part of the core. This is about significantly smaller than the discs that would form if angular momentum was conserved.
The analytical predictions are confronted against a large sample of 3D, non-ideal MHD collapse calculations covering variations of a factor 100 in core mass, a factor 10 in the level of turbulence, a factor 5 in rotation, and magnetic mass-to-flux over critical mass-to-flux ratios 2 and 5. The disc radius estimates are found to agree with the numerical simulations within less than a factor 2.
A striking prediction of our analysis is the weak dependence of circumstellar disc radii upon the various relevant quantities, suggesting weak variations among class-0 disc sizes. In some cases, we note the onset of large spiral arms beyond this radius.
BISTRO Survey: Gravity-Dominated and Magnetically Regulated Star Formation in M17 SW
Nanjing University（南京大学）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（现代天文学与天体物理学教育部重点实验室（南京大学））；Korea Astronomy and Space Science Institute（韩国天文与空间科学研究所）；Xinjiang Astronomical Observatory, Chinese Academy of Sciences（中国科学院新疆天文台）；Cardiff University（卡迪夫大学）；Jeremiah Horrocks Institute, University of Lancashire（兰开斯特大学杰里迈亚·霍罗克斯研究所）；Department of Astronomy, Graduate School of Science, The University of Tokyo（东京大学理学研究科天文学专业）；University of Science and Technology, Korea (UST)（韩国科学技术院）
Magneto-Gravitational Regulated Streamer Accretion onto a Class 0 Protostellar System
Institut de Ciències de l'Espai (ICE-CSIC)（太空科学研究所）；Korea Astronomy and Space Science Institute（韩国天文学与空间科学研究院）；Institut d'Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究学院）；Worcester State University（伍斯特州立大学）；University of Toledo（托莱多大学）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）；National Radio Astronomy Observatory（美国国家射电天文台）；Joint ALMA Observatory（ALMA联合天文台）；Instituto Argentino de Radioastronomía（阿根廷射电天文研究所）；Universidad Nacional de La Plata（拉普拉塔国立大学）；University of Virginia（弗吉尼亚大学）；University of Illinois（伊利诺伊大学）；Academia Sinica Institute of Astronomy and Astrophysics（中央研究院天文及天文物理研究所）；Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理研究所）；The University of Tokyo（东京大学）；Queen’s University（女王大学）；Center for Astrophysics | Harvard & Smithsonian（哈佛史密森尼天体物理中心）；AES Indiana（AES印第安纳）；National Astronomical Observatory of Japan（日本国立天文台）；Space Science Institute（空间科学研究所）；Guangxi University（广西大学）
The dominance of turbulence over magnetism in the formation of massive star cluster seeds
Nanjing University（南京大学）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（教育部现代天文与天体物理重点实验室（南京大学））；National Astronomical Observatory of Japan（日本国立天文台）；The University of Tokyo（东京大学）；Academia Sinica, Institute of Astronomy and Astrophysics（中央研究院天文及天文物理研究所）；Center for Astrophysics — Harvard & Smithsonian（哈佛史密森尼天体物理中心）；Institut de Ciencies de l’Espai (ICE, CSIC)（空间科学研究所（加泰罗尼亚高等研究理事会））；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究研究所）
Magnetic Fields in Massive Star-forming Regions (MagMaR). VII. On the dynamical importance of B-fields in massive protocluster W33 A
Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；Center for Astrophysics | Harvard & Smithsonian（哈佛史密森尼天体物理中心）；Department of Astronomy, Graduate School of Science, The University of Tokyo（东京大学大学院理学系研究科天文学专攻）；Department of Physics, National Sun Yat-Sen University（国立中山大学物理系）；Center of Astronomy and Gravitation, National Taiwan Normal University（国立台湾师范大学天文重力研究中心）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Joint ALMA Observatory（ALMA联合机构）；National Radio Astronomy Observatory（美国国家射电天文台）；Academia Sinica Institute of Astronomy and Astrophysics（中央研究院天文及天文物理研究所）
