Recent progress with observations and models to characterize the magnetic fields from star-forming cores to protostellar disks

Abstract

In this review article, we aim at providing a global outlook on the progresses made in the recent years to characterize the role of magnetic fields during the embedded phases of the star formation process. Thanks to the development of observational capabilities and the parallel progress in numerical models, capturing most of the important physics at work during star formation; it has recently become possible to confront detailed predictions of magnetized models to observational properties of the youngest protostars. We provide an overview of the most important consequences when adding magnetic fields to state-of-the-art models of protostellar formation, emphasizing their role to shape the resulting star(s) and their disk(s). We discuss the importance of magnetic field coupling to set the efficiency of magnetic processes and provide a review of observational works putting constraints on the two main agents responsible for the coupling in star-forming cores: dust grains and ionized gas. We recall the physical processes and observational methods, which allow to trace the magnetic field topology and its intensity in embedded protostars and review the main steps, success, and limitations in comparing real observations to synthetic observations from the non-ideal MHD models. Finally, we discuss the main threads of observational evidence that suggest a key role of magnetic fields for star and disk formation, and propose a scenario solving the angular momentum for star formation, also highlighting the remaining tensions that exist between models and observations.

Protoplanetary Disk Size under Nonideal Magnetohydrodynamics: A General Formalism with Inclined Magnetic Field

“…This effect is even more pronounced for highermass and more-magnetized disks (represented by large r h /r v ). This is probably the reason why large disks are rare from observations (Maury et al 2022).…”

“…One major conclusion is that disks seem to be small with size not exceeding 50 au at this stage. However, there have yet been strong conclusive results on whether the orientation of the magnetic field is correlated with the disk rotation axis (see reviews, e.g., Maury et al 2022;Tsukamoto et al 2023, and references therein). The disk size at this stage is regulated by its magnetic interaction with the accreting envelope, and some scaling relations has been suggested assuming aligned field and rotation (Hennebelle et al 2016).…”

Protostellar Chimney Flues: Are Jets and Outflows Lifting Submillimeter Dust Grains from Disks into Envelopes?

“…We notice that the three sources of our sample with the largest outflow mass loss rates ( 2 ×10 −7 M e yr −1 ) have β < 0.8. If we consider this value in Equation 3, and we fix M * = 1 M e , T gas = 20 K at the outflow's base, r = 1 au, z/r = 0.1, r + = 50 au (typical Class 0 disk radius, e.g., Maury et al 2022), and r − = 0.1 au, we obtain a 150 m max m  . Since outflow mass loss rates are lower limits due to optical depth effects, a max could be higher by even an order of magnitude.…”

On the Magnetic Field Properties of Protostellar Envelopes in Orion

“…Magnetic fields (henceforth B-fields) are thought to play a crucial role in the star-forming processes (e.g., Maury et al 2022;Pattle et al 2023). In ideal MHD models, during the collapse phase of a prestellar core, the B-field lines are drawn Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.…”