RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: NONIDEAL MAGNETOHYDRODYNAMIC EFFECTS AND EARLY FORMATION OF CIRCUMSTELLAR DISKS

By K. Tomida, S. Okuzumi, Masahiro N. Machida. 2015

141 citations recorded by the source corpus.

The transport of angular momentum by magnetic fields is a crucial physical process in the formation and evolution of stars and disks. Because the ionization degree in star-forming clouds is extremely low, nonideal magnetohydrodynamic (MHD) effects such as ambipolar diffusion and ohmic dissipation work strongly during protostellar collapse. These effects have significant impacts in the early phase of star formation as they redistribute magnetic flux and suppress angular momentum transport by magnetic fields. We perform three-dimensional nested-grid radiation magnetohydrodynamic simulations including ohmic dissipation and ambipolar diffusion. Without these effects, magnetic fields transport angular momentum so efficiently that no rotationally supported disk is formed even after the second collapse. Ohmic dissipation works only in a relatively high density region within the first core and suppresses angular momentum transport, enabling formation of a very small rotationally supported disk after the second collapse. With both ohmic dissipation and ambipolar diffusion, these effects work effectively in almost the entire region within the first core and significant magnetic flux loss occurs. As a result, a rotationally supported disk is formed even before a protostellar core forms. The size of the disk is still small, about 5 AU at the end of the first core phase, but this disk will grow later as gas accretion continues. Thus, the nonideal MHD effects can resolve the so-called magnetic braking catastrophe while keeping the disk size small in the early phase, which is implied from recent interferometric observations.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/3c877446576eeba0df16fda95e87e22574aa56fd

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Citations in the corpus

Ambipolar diffusion in low-mass star formation - I. General comparison with the ideal magnetohydrodynamic case (2015, background): “The region above and below the core is strongly depleted, leading to a highly magnetised and low-density region (ρ < 10−16 g cm−3, B > 10−2 G) that corresponds to the polar cavity mentioned in Tomida et al. (2015).”
On the diversity and statistical properties of protostellar discs (2018, background): “…by magnetic braking in ideal MHD calculations, the effects of introducing ambipolar diffusion alone are insufficient to allow the formation of large discs (Duffin & Pudritz 2009; Mellon & Li 2009; Li et al. 2011; Dapp et al. 2012; Tomida et al. 2015; Tsukamoto et al. 2015b; Wurster et al. 2016).”
The Athena++ Adaptive Mesh Refinement Framework: Design and Magnetohydrodynamic Solvers (2020, methodology): “…reduce the symmetry in the problem, a two-dimensional domain of [−0.5, 0.5] × [−0.0078125, 0.0078125] with resolution of 1/128 is used, with the initial interface rotated by an angle θ = tan−1(3/4) using shifted-periodic boundary condition in the y-direction (see Tomida et al. 2015, Appendix A.6).”
Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics (2017, background): “…follows from protostellar core collapse, and it is well known that non-ideal MHD effects play an important role throughout the processes of core collapse and disk formation (see Li et al. 2014 for a review, and more recent works by Tomida et al. 2015; Tsukamoto et al. 2015; Wurster et al. 2016).”