Collapse of Magnetized Singular Isothermal Toroids. II. Rotation and Magnetic Braking

By A. Allen, Zhi-Yun Li, F. Shu. 2003

221 citations recorded by the source corpus.

We study numerically the collapse of rotating magnetized molecular cloud cores, focusing on rotation and magnetic braking during the main accretion phase of isolated star formation. Motivated by previous numerical work and analytic considerations, we idealize the precollapse core as a magnetized singular isothermal toroid, with a constant rotational speed everywhere. The collapse starts from the center and propagates outward in an inside-out fashion, satisfying exact self-similarity in space and time. For rotation rates and field strengths typical of dense low-mass cores, the main feature remains the flattening of the mass distribution along field lines—the formation of a pseudodisk, as in the nonrotating cases. The density distribution of the pseudodisk is little affected by rotation. On the other hand, the rotation rate is strongly modified by pseudodisk formation. Most of the centrally accreted material reaches the vicinity of the protostar through the pseudodisk. The specific angular momentum can be greatly reduced on the way, by an order of magnitude or more, even when the precollapse field strength is substantially below the critical value for dominant cloud support. The efficient magnetic braking is due to the pinched geometry of the magnetic field in the pseudodisk, which strengthens the magnetic field and lengthens the level arm for braking. Both effects enhance the magnetic transport of angular momentum from inside to outside. The excess angular momentum is carried away in a low-speed outflow that has, despite claims made by other workers, little in common with observed bipolar molecular outflows. We discuss the implications of our calculations for the formation of true disks that are supported against gravity by rotation.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/9b1c81bbc36277b3c2dfc7390f162fa31f568318

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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): “…result of the very effective magnetic braking created by a strong pile-up of magnetic flux towards the centre of the collapsing system (Galli et al. 2006, Allen et al. 2003, Price & Bate 2007; Hennebelle & Teyssier 2008; Matsumoto & Tomisaka 2004; Hennebelle & Fromang 2008; Commerçon et al. 2010).”
NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION (2011, background): “This was first demonstrated in Allen et al. (2003), who carried out 2D (axisymmetric) simulations of the collapse of rotating cores magnetized to a level of λ ≤ 10.”
Disk formation during collapse of magnetized protostellar cores (2009, background): “2006) which transports angular momentum from the inner parts of the cloud towards its outer regions (Allen et al. 2003, Fromang et al. 2006, Price & Bate 2007, Hennebelle & Fromang 2008 (hereafter HF08), Mellon & Li 2008, 2009).”
Accretion disks in luminous young stellar objects (2015, methodology): “However, when Vrot is not reported, we have estimated it from the maps of the velocity gradient shown in the papers.”
Protostellar disk formation and transport of angular momentum during magnetized core collapse (2012, background): “Theoretically, the presence of a magnetic field of such intensities has been found to modify substantially the collapse (Allen et al. 2003; Machida et al. 2005; Fromang et al. 2006) and in particular the formation of disks.”
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: NONIDEAL MAGNETOHYDRODYNAMIC EFFECTS AND EARLY FORMATION OF CIRCUMSTELLAR DISKS (2015, background): “…at least in the early phase of star formation and with the ideal magnetohydrodynamic (MHD) approximation, which is called the magnetic braking catastrophe (e.g., Mestel & Spitzer 1956; Allen et al. 2003; Mellon & Li 2008; Li et al. 2011, 2014b) or fragmentation crisis (Hennebelle & Teyssier 2008).”
Outflows and Jets from Collapsing Magnetized Cloud Cores (2005, background): “Such large scale, low velocity outflows are also seen in other collapse simulations (e.g., Tomisaka 1998, 2002; Allen et al. 2003).”
Magnetic processes in a collapsing dense core I. Accretion and ejection (2007, methodology): “…power and the improvement of the numerical schemes, recent developments have been realized and various 2D (Nakamura et al. 1995, Tomisaka 1998, Allen et al. 2003) as well as 3D numerical calculations have been performed (Hosking & Whitworth 2004, Machida et al. 2005, 2007, Ziegler 2005,…”
PICO: Probe of Inflation and Cosmic Origins (2019, background): “By comparing the orientation of the core-scale magnetic fields with the orientation and sizes of proto-planetary disks, PICO will probe whether magnetic braking influences the growth of such disks [169, 170] and provide complementarity to higher angular resolution instruments such as ALMA and SOFIA ”
TADPOL: A 1.3 mm SURVEY OF DUST POLARIZATION IN STAR-FORMING CORES AND REGIONS (2013, background): “Objects with misaligned B-fields and rotation axes are less susceptible to the “magnetic braking catastrophe,” where magnetic braking prevents the formation of a rotationally supported Keplerian disk (Allen et al. 2003; Li et al. 2011).”
On the diversity and statistical properties of protostellar discs (2018, background): “…geometries where the axis of rotation of a core is aligned with a global field that is anchored at large distances from the centre of the core (Allen et al. 2003; Galli et al. 2006; Price & Bate 2007; Mellon & Li 2008; Hennebelle & Fromang 2008; Duffin & Pudritz 2009; Dapp & Basu 2010;…”
Collapse, outflows and fragmentation of massive, turbulent and magnetized prestellar barotropic cores (2011, result): “This is at variance with the conclusion that even low values of the magnetic field could entirely suppress the formation of a disk, as previously inferred by Allen et al. (2003), Galli et al. (2006), Price & Bate (2007), Hennebelle & Fromang (2008), and Mellon & Li (2008, 2009).”
Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A Grid of 200,000 YSO Model SEDs (2006, background): “…because rotation and free-fall likely dominate over magnetic effects (Galli & Shu 1993; Desch & Mouschovias 2001; Nakamura et al. 1999) (though see Allen et al. (2003) for a discussion of magnetic braking), and observations of radial intensity profiles are consistent with free-fall collapse…”