Magnetic Braking and Protostellar Disk Formation: The Ideal MHD Limit

By R. Mellon, Zhi-Yun Li. 2007

218 citations recorded by the source corpus.

Magnetic fields are usually considered dynamically important in star formation when the dimensionless mass-to-flux ratio is close to, or less than, unity (λ ≲ 1). We show that, in disk formation, the requirement is far less stringent. This conclusion is drawn from a set of 2D (axisymmetric) simulations of the collapse of rotating, singular isothermal cores magnetized to different degrees. We find that a weak field corresponding to λ ∼ 100 can begin to disrupt the rotationally supported disk through magnetic braking, by creating regions of rapid, supersonic collapse in the disk. These regions are separated by one or more centrifugal barriers, where the rapid infall is temporarily halted. The number of centrifugal barriers increases with the mass-to-flux ratio λ. When λ ≳ 100, they merge together to form a more or less contiguous, rotationally supported disk. Even though the magnetic field in such a case is extremely weak on the scale of dense cores, it is amplified by collapse and differential rotation, to the extent that its pressure dominates the thermal pressure in both the disk and its surrounding region. For relatively strongly magnetized cores with λ ≲ 10, the disk formation is suppressed completely, as found previously. A new feature is that the mass accretion is highly episodic, due to reconnection of the magnetic field lines accumulated near the center. For rotationally supported disks to appear during the protostellar mass accretion phase of star formation in dense cores with realistic field strengths, the powerful magnetic brake must be weakened, perhaps through nonideal MHD effects. Another possibility is to remove, through protostellar winds, the material that acts to brake the disk rotation. We discuss the possibility of observing a generic product of the magnetic braking, an extended circumstellar region that is supported by a combination of toroidal magnetic field and rotation—a “magnetogyrosphere”—interferometrically.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/3ea4f73f3d9f88c24f4179480cd83271b55becde

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Citations in the corpus

Effect of Magnetic Braking on Circumstellar Disk Formation in a Strongly Magnetized Cloud (2010, methodology): “Using an ideal MHD calculation, Mellon & Li (2008) showed that the circumstellar disk formed in a magnetized cloud has a size of ∼ 10AU at maximum.”
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).”
Magnetic Fields of Nondegenerate Stars (2009, methodology): “…have been carried out in recent years primarilyfor low-mass stars (e.g., Machida et al. 2004; Banerjee & Pudritz 2006; Hennebelle & Fromang 2008; Mellon & Li 2008), and in a few cases for massive stars as well (e.g., Banerjee & Pudritz 2007), mostly using numerical techniques such as adaptive…”
Protostellar disk formation and transport of angular momentum during magnetized core collapse (2012, methodology): “5 − 10, Mellon & Li 2008; Price & Bate 2007; Hennebelle & Fromang 2008).”
Collapse, outflows and fragmentation of massive, turbulent and magnetized prestellar barotropic cores (2011, background): “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).”
A Keplerian disk around a Class 0 source: ALMA observations of VLA1623A (2013, background): “Ideal MHD shows that magnetic field breaking can hinder disk formation (Mellon & Li 2008); however, if the magnetic Appendices are available in electronic form at http://www.aanda.org field and rotation axes are misaligned, rotationally supported disks may form since the magnetic breaking…”
OUTFLOW FEEDBACK REGULATED MASSIVE STAR FORMATION IN PARSEC-SCALE CLUSTER-FORMING CLUMPS (2009, background): “Magnetic braking driven bubbles provide a form of energy feedback that should accompany any star formed in a magnetized cloud (e.g., Draine 1980; Tomisaka 1998; Banerjee & Pudritz 2006; Mellon & Li 2008; Hennebelle & Fromang 2008) but is absent from purely hydrodynamic models.”
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: PROTOSTELLAR CORE FORMATION (2012, background): “Moreover, Mellon & Li (2008, 2009) claimed that rotationally supported circumstellar disks are difficult to form in magnetized molecular cloud cores because the angular momentum transport due to magnetic fields is too efficient (“the magnetic braking catastrophe”; see also Li et al. 2011).”
NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION (2011, methodology): “The expected numerical reconnection is present in the ideal MHD simulations of Mellon & Li (2008), especially for relatively strongly magnetized cores (with a dimensionless mass-to-flux λ of several or less; see their Figs.”
Disk formation during collapse of magnetized protostellar cores (2009, background): “As shown in HF08, for values of µ lower than 5, the magnetic pressure produces a very significant density enhancement (typically a factor 10 or more) in the equatorial plane and very stiff gradients along the z direction.”
ANALYTICAL THEORY FOR THE INITIAL MASS FUNCTION. II. PROPERTIES OF THE FLOW (2009, background): “…magnetic field, which has been shown to severely inhibit disk fragmentation (Machida et al. 2005, 2008, Hennebelle & Teyssier 2008, Price & Bate 2008) or even to prevent disk formation by magnetic braking (Galli et al. 2006, Price & Bate 2007, Hennebelle & Fromang 2008, Mellon & Li 2008a,b).”
A millimeter Continuum Size–Luminosity Relationship for Protoplanetary Disks (2017, background): “Disk sizes reflect some convolution of the processes involved in formation (Galli et al. 2006; Mellon & Li 2008; Vorobyov 2009; Dapp & Basu 2010; Machida et al. 2011), evolution of angular momentum (e.g., Lynden-Bell & Pringle 1974; Hartmann et al. 1998), and, perhaps most importantly, the growth…”
On the diversity and statistical properties of protostellar discs (2018, background): “…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; Machida et al. 2011; Li et al. 2011; Dapp et al. 2012).”
Our astrochemical heritage (2012, background): “…simulations of collapsing cores (e.g., Allen 4IMHD assumes that the mass to magnetic-flux ratio is constant, which implies that magnetic field lines follow the gas motions, i.e. the magnetic field is “frozen” into the neutral medium. et al. 2003; Mellon and Li 2008; Hennebelle and Fromang 2008).”