Magnetic Braking and Protostellar Disk Formation: Ambipolar Diffusion

Mellon, Richard R.; Li, Zhi-Yun

doi:10.1088/0004-637x/698/1/922

Cited by 148 publications

(196 citation statements)

References 39 publications

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“…When α = 90 • , we find that disks may form for smaller values of μ, as long as μ > 2−3, and for even lower values of μ, disk formation does not seem to be possible. Nevertheless, for these highly magnetized configurations, the question of whether a disk may form at later times, or because of non-ideal MHD effects (Hosking & Whitworth 2004;Machida et al 2008;Mellon & Li 2009), remains unanswered. We recall that although Belloche et al (2002) observe a significant amount of rotation in the envelope of IRAM04191, they exclude a disk of size larger than 20 AU.…”

Section: Resultsmentioning

confidence: 99%

“…Magnetohydrodynamic (MHD) simulations (e.g., Machida et al 2005;Banerjee & Pudritz 2006) find that even for modest values of the magnetic intensity, disk formation can be suppressed by magnetic braking (Shu et al 1987;Mouschovias 1991;Basu & Mouschovias 1995;Galli et al 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). …”

Section: Introductionmentioning

confidence: 99%

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Disk formation during collapse of magnetized protostellar cores

Hennebelle¹,

Ciardi

2009

A&A

224

255

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Context. In the context of star and planet formation, understanding the formation of disks is of fundamental importance. Aims. Previous studies found that the magnetic field has a very strong impact on the collapse of a prestellar cloud, by possibly suppressing the formation of a disk even for relatively modest values of the magnetic intensity. Since observations infer that cores have a substantial level of magnetization, this raises the question of how disks form. However, most studies have been restricted to the case in which the initial angle, α, between the magnetic field and the rotation axis equals 0 • . Here we explore and analyse the influence of non aligned configurations on disk formation. Methods. We perform 3D ideal MHD, AMR numerical simulations for various values of μ, the ratio of the mass-to-flux to the critical mass-to-flux, and various values of α. Results. We find that disks form more easily as α increases from 0 to 90 • . We propose that as the magnetized pseudo-disks become thicker with increasing α, the magnetic braking efficiency is lowered. We also find that even small values of α ( 10-20 • ) show significant differences with the aligned case. Conclusions. Within the framework of ideal MHD, and for our choice of initial conditions, centrifugally supported disks cannot form for values of μ smaller than 3 when the magnetic field and the rotation axis are perpendicular, and smaller than about 5-10 when they are perfectly aligned.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Disk formation during collapse of magnetized protostellar cores

Hennebelle¹,

Ciardi

2009

A&A

224

255

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“…Ambipolar diffusion (e.g. Mellon & Li 2009;Duffin & Pudritz 2009), however, does not result in the formation of Keplerian discs in the earliest phase of protostellar evolution. Furthermore, including Ohmic dissipation seems to allow only for very small (∼ 10 solar radii) rotationally supported structures (e.g.…”

Section: Introductionmentioning

confidence: 99%

Accretion and magnetic field morphology around Class 0 stage protostellar discs

Seifried

Banerjee

Pudritz

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We analyse simulations of turbulent, magnetised molecular cloud cores focussing on the formation of Class 0 stage protostellar discs and the physical conditions in their surroundings. We show that for a wide range of initial conditions Keplerian discs are formed in the Class 0 stage already. In particular, we show that even subsonic turbulent motions reduce the magnetic braking efficiency sufficiently in order to allow rotationally supported discs to form. We therefore suggest that already during the Class 0 stage the fraction of Keplerian discs is significantly higher than 50%, consistent with recent observational trends but significantly higher than predictions based on simulations with misaligned magnetic fields, demonstrating the importance of turbulent motions for the formation of Keplerian discs. We show that the accretion of mass and angular momentum in the surroundings of protostellar discs occurs in a highly anisotropic manner, by means of a few narrow accretion channels. The magnetic field structure in the vicinity of the discs is highly disordered, revealing field reversals up to distances of 1000 AU. These findings demonstrate that as soon as even mild turbulent motions are included, the classical disc formation scenario of a coherently rotating environment and a well-ordered magnetic field breaks down. Hence, it is highly questionable to assess the magnetic braking efficiency based on non-turbulent collapse simulation. We strongly suggest that, in addition to the global magnetic field properties, the small-scale accretion flow and detailed magnetic field structure have to be considered in order to assess the likelihood of Keplerian discs to be present.

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“…This is because the angular momentum that could lead to the formation of a disk thin enough for fragmentation to occur is transferred by magnetic braking and the protostellar outflow (see, §4). Thus, in a strongly magnetized cloud, no thin disk appears (Mellon & Li 2009) and, therefore, no fragmentation occurs. Figure 1 shows the rotation and magnetic field conditions under 68 Masahiro N. Machida Inside the purple surfaces, the flow is outflowing from the central object (the first core or protostar), and outside the purple surface (in the blue regions), the flow is inflowing to the central object.…”

Section: Fragmentation and Binary Formationmentioning

confidence: 99%

Recent Developments in Simulations of Low-mass Star Formation

Machida¹

2010

Proc. IAU

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Abstract. In star forming regions, we can observe different evolutionary stages of various objects and phenomena such as molecular clouds, protostellar jets and outflows, circumstellar disks, and protostars. However, it is difficult to directly observe the star formation process itself, because it is veiled by the dense infalling envelope. Numerical simulations can unveil the star formation process in the collapsing gas cloud. Recently, some studies showed protostar formation from the prestellar core stage, in which both molecular clouds and protostars are resolved with sufficient spatial resolution. These simulations showed fragmentation and binary formation, outflow and jet driving, and circumstellar disk formation in the collapsing gas clouds. In addition, the angular momentum transfer and dissipation process of the magnetic field in the star formation process were investigated. In this paper, I review recent developments in numerical simulations of lowmass star formation.

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Magnetic Braking and Protostellar Disk Formation: Ambipolar Diffusion

Cited by 148 publications

References 39 publications

Disk formation during collapse of magnetized protostellar cores

Disk formation during collapse of magnetized protostellar cores

Accretion and magnetic field morphology around Class 0 stage protostellar discs

Recent Developments in Simulations of Low-mass Star Formation

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