Disk Formation in Magnetized Clouds Enabled by the Hall Effect

Krasnopolsky, Ruben; Li, Zhi-Yun; Shang, Hsien

doi:10.1088/0004-637x/733/1/54

Cited by 102 publications

(128 citation statements)

References 25 publications

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“…This poses further problems to disk formation in previous numerical studies of collapse and disk formation. On the other hand, the inclusion of the Hall effect does not require a rotating envelope core to form a rotating structure (e.g., Krasnopolsky et al 2011;Li et al 2011). Further studies are required to compare the expected observables from rotating and non-rotating models.…”

Section: On the Large-scale Rotationmentioning

confidence: 99%

Rotationally-supported disks around Class I sources in Taurus: disk formation constraints

Harsono

Jørgensen

Dishoeck

et al. 2014

A&A

129

169

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Context. Disks are observed around pre-main sequence stars, but how and when they form is still heavily debated. While disks around young stellar objects have been identified through thermal dust emission, spatially and spectrally resolved molecular line observations are needed to determine their nature. Only a handful of embedded rotationally supported disks have been identified to date. Aims. We identify and characterize rotationally supported disks near the end of the main accretion phase of low-mass protostars by comparing their gas and dust structures. Methods. Subarcsecond observations of dust and gas toward four Class I low-mass young stellar objects in Taurus are presented at significantly higher sensitivity than previous studies. The 13 CO and C 18 O J = 2-1 transitions at 220 GHz were observed with the Plateau de Bure Interferometer at a spatial resolution of ≤0.8 (56 AU radius at 140 pc) and analyzed using uv-space position velocity diagrams to determine the nature of their observed velocity gradient. Results. Rotationally supported disks (RSDs) are detected around 3 of the 4 Class I sources studied. The derived masses identify them as Stage I objects; i.e., their stellar mass is higher than their envelope and disk masses. The outer radii of the Keplerian disks toward our sample of Class I sources are ≤100 AU. The lack of on-source C 18 O emission for TMR1 puts an upper limit of 50 AU on its size. Flattened structures at radii >100 AU around these sources are dominated by infalling motion (υ ∝ r −1 ). A large-scale envelope model is required to estimate the basic parameters of the flattened structure from spatially resolved continuum data. Similarities and differences between the gas and dust disk are discussed. Combined with literature data, the sizes of the RSDs around Class I objects are best described with evolutionary models with an initial rotation of Ω = 10 −14 Hz and slow sound speeds. Based on the comparison of gas and dust disk masses, little CO is frozen out within 100 AU in these disks. Conclusions. Rotationally supported disks with radii up to 100 AU are present around Class I embedded objects. Larger surveys of both Class 0 and I objects are needed to determine whether most disks form late or early in the embedded phase.

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Section: On the Large-scale Rotationmentioning

confidence: 99%

Rotationally-supported disks around Class I sources in Taurus: disk formation constraints

Harsono

Jørgensen

Dishoeck

et al. 2014

A&A

129

169

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“…In the simplest case of electron-ion-neutral fluid, the spinup is caused by the current carriers (the electrons) moving in the azimuthal direction, generating a magnetic torque through field twisting; the toroidal current is produced by gravitational collapse, which drags the poloidal field into a pinched, hourglass-like configuration. The Hall spinup was studied numerically by Krasnopolsky et al (2011) and semi-analytically by Braiding & Wardle (2012a,b). Krasnopolsky et al (2011) showed that a rotationally sup-ported disk can form even in an initially non-rotating core, provided that the Hall coefficient is large enough.…”

Section: Non-ideal Mhd Effectsmentioning

confidence: 99%

The Earliest Stages of Star and Planet Formation: Core Collapse, and the Formation of Disks and Outflows

Li¹,

Banerjee²,

Jørgensen³

et al. 2014

Protostars and Planets VI

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The formation of stars and planets are connected through disks. Our theoretical understanding of disk formation has undergone drastic changes in recent years, and we are on the brink of a revolution in disk observation enabled by ALMA. Large rotationally supported circumstellar disks, although common around more evolved young stellar objects, are rarely detected during the earliest, "Class 0" phase; a few excellent candidates have been discovered recently around both low-and high-mass protostars though. In this early phase, prominent outflows are ubiquitously observed; they are expected to be associated with at least small magnetized disks. Whether the paucity of large Keplerian disks is due to observational challenges or intrinsically different properties of the youngest disks is unclear. In this review we focus on the observations and theory of the formation of early disks and outflows, and their connections with the first phases of planet formation. Disk formation -once thought to be a simple consequence of the conservation of angular momentum during hydrodynamic core collapse -is far more subtle in magnetized gas. In this case, the rotation can be strongly magnetically braked. Indeed, both analytic arguments and numerical simulations have shown that disk formation is suppressed in the strict ideal magnetohydrodynamic (MHD) limit for the observed level of core magnetization. We review what is known about this "magnetic braking catastrophe", possible ways to resolve it, and the current status of early disk observations. Possible resolutions include non-ideal MHD effects (ambipolar diffusion, Ohmic dissipation and Hall effect), magnetic interchange instability in the inner part of protostellar accretion flow, turbulence, misalignment between the magnetic field and rotation axis, and depletion of the slowly rotating envelope by outflow stripping or accretion. Outflows are also intimately linked to disk formation; they are a natural product of magnetic fields and rotation and are important signposts of star formation. We review new developments on early outflow generation since PPV. The properties of early disks and outflows are a key component of planet formation in its early stages and we review these major connections.

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“…Magnetic fields are also believed to be of key importance during the star-formation process (Hennebelle & Fromang 2008;Hennebelle & Ciardi 2009;Commerçon et al 2010;Hennebelle et al 2011;Seifried et al 2011;Joos et al 2012). Even if diffusion is required to remove much of the magnetic flux during that process (Mellon & Li 2009;Krasnopolsky et al 2010Krasnopolsky et al , 2011Li et al 2011;Santos-Lima et al 2012;Dapp et al 2012), it is plausible that some net poloidal flux is retained and carried down to the scale of the disk during its formation. The resulting strength of that potential magnetic field is highly uncertain, but might be in the approximate range 10 −2 to a few Gauss (Wardle 2007).…”

Section: Introductionmentioning

confidence: 99%

Local outflows from turbulent accretion disks

Fromang

Latter

Lesur

et al. 2013

A&A

143

168

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Aims. The aim of this paper is to investigate the properties of accretion disks threaded by a weak vertical magnetic field, with a particular focus on the interplay between magnetohydrodynamic (MHD) turbulence driven by the magnetorotational instability (MRI) and outflows that might be launched from the disk. Methods. For that purpose, we use a set of numerical simulations performed with the MHD code RAMSES in the framework of the shearing box model. We concentrate on the case of a rather weak vertical magnetic field such that the initial ratio β 0 of the thermal and magnetic pressures in the disk midplane equals 10 4 . Results. As reported recently, we find that MHD turbulence drives an efficient outflow out of the computational box. We demonstrate a strong sensitivity of that result to the box size: enlargements in the radial and vertical directions lead to a reduction of up to an order of magnitude in the mass-loss rate. Such a dependence prevents any realistic estimates of disk mass-loss rates being derived using shearing-box simulations. We find however that the flow morphology is robust and independent of the numerical details of the simulations. Its properties display some features and approximate invariants that are reminiscent of the Blandford & Payne launching mechanism, but differences exist. For the magnetic field strength considered in this paper, we also find that angular momentum transport is most likely dominated by MHD turbulence, the saturation of which scales with the magnetic Prandtl number, the ratio of viscosity and resistivity, in a way that is in good agreement with expectations based on unstratified simulations. Conclusions. This paper thus demonstrates for the first time that accretion disks can simultaneously exhibit MRI-driven MHD turbulence along with magneto-centrifugally accelerated outflows. However, in contradiction with previously published results, such outflows probably have little impact on the disk dynamics.

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Disk Formation in Magnetized Clouds Enabled by the Hall Effect

Cited by 102 publications

References 25 publications

Rotationally-supported disks around Class I sources in Taurus: disk formation constraints

Rotationally-supported disks around Class I sources in Taurus: disk formation constraints

The Earliest Stages of Star and Planet Formation: Core Collapse, and the Formation of Disks and Outflows

Local outflows from turbulent accretion disks

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