Protostellar disk formation and transport of angular momentum during magnetized core collapse

Joos, Marc; Hennebelle, P.; Ciardi, A.

doi:10.1051/0004-6361/201118730

Cited by 286 publications

(510 citation statements)

References 51 publications

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“…Said in a different way, in the λ = 8.38 model a particle "sees" a larger amount of N(H 2 ) and it loses more energy than in the flatter λ = 1.63 model where the density along the field direction increases only close to the cloud's midplane. Joos et al 2012): mass-to-flux ratio, initial angle between the magnetic field direction and the rotation axis, time after the formation of the first Larson's core (core formed in the centre of the pseudo-disc with n 10 10 cm −3 and r ∼ 10−20 AU), maximum mass of the protostellar core and of the disc. Last column gives information about the disc formation.…”

Section: Dependence Of ζ H 2 On the Density Profilementioning

confidence: 99%

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Cosmic-ray ionisation in collapsing clouds

Padovani

Hennebelle

Galli

2013

A&A

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104

118

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Context. Cosmic rays play an important role in dense molecular cores, affecting their thermal and dynamical evolution and initiating the chemistry. Several studies have shown that the formation of protostellar discs in collapsing clouds is severely hampered by the braking torque exerted by the entrained magnetic field on the infalling gas, as long as the field remains frozen to the gas. Aims. In this paper we examine the possibility that the concentration and twisting of the field lines in the inner region of collapse can produce a significant reduction of the ionisation fraction. Methods. To check whether the cosmic-ray ionisation rate can fall below the critical value required to maintain good coupling, we first study the propagation of cosmic rays in a model of a static magnetised cloud varying the relative strength of the toroidal/poloidal components and the mass-to-flux ratio. We then follow the path of cosmic rays using realistic magnetic field configurations generated by numerical simulations of a rotating collapsing core with different initial conditions. Results. We find that an increment of the toroidal component of the magnetic field, or, in general, a more twisted configuration of the field lines, results in a decrease in the cosmic-ray flux. This is mainly due to the magnetic mirroring effect that is stronger where larger variations in the field direction are present. In particular, we find a decrease of the cosmic-ray ionisation rate below 10 −18 s −1 in the central 300-400 AU, where density is higher than about 10 9 cm −3 . This very low value of the ionisation rate is attained in the cases of intermediate and low magnetisation (mass-to-flux ratio λ = 5 and 17, respectively) and for toroidal fields larger than about 40% of the total field. Conclusions. Magnetic field effects can significantly reduce the ionisation fraction in collapsing clouds. We provide a handy fitting formula to compute approximately the attenuation of the cosmic-ray ionisation rate in a molecular cloud as a function of the density and the magnetic configuration.

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Section: Dependence Of ζ H 2 On the Density Profilementioning

confidence: 99%

“…We select a series of simulations from Joos et al (2012) varying the mass-toflux ratio λ and the angle between the initial magnetic field direction and the initial rotation axis α B,J . Table 1 lists the parameters.…”

Section: Numerical Modelsmentioning

confidence: 99%

Cosmic-ray ionisation in collapsing clouds

Padovani

Hennebelle

Galli

2013

A&A

Self Cite

104

118

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“…Recently, it was shown that a magnetic field inclined with respect to the rotation of the core can result in the formation of rotationally supported discs (Hennebelle & Ciardi 2009;Ciardi & Hennebelle 2010;Joos et al 2012). Based on these simulations and observational results, Krumholz et al (2013) showed, however, that this would result in a fraction of Keplerian discs in the Class 0 stage of about 10% (at the very most 50%).…”

Section: Misaligned Magnetic Fieldsmentioning

confidence: 99%

“…On the other hand, Hennebelle & Ciardi (2009), Ciardi & Hennebelle (2010) and Joos et al (2012) performed simulations deviating from the highly idealised setup of a uniformly rotating core and a magnetic field parallel to the rotation axis were performed. The authors could show that for an overall magnetic field inclined to the core's rotation axis the formation of rotationally supported discs is possible.…”

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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“…In the standard star formation picture, the infalling material forms an accretion disk simply from angular momentum conservation (e.g., Lin & Pringle 1990;Bodenheimer 1995;Belloche 2013). However, magnetic field strengths observed toward molecular cores (see Crutcher 2012, for a recent review) are expected theoretically to be sufficient in affecting the formation and evolution of disks around low-mass stars (e.g., Galli et al 2006;Joos et al 2012;Krumholz et al 2013;Li et al 2013Li et al , 2014a. Recent advances in both observational and theoretical studies give an opportunity to test the star formation process at small scales (<1000 AU).…”

Section: Introductionmentioning

confidence: 99%

Testing protostellar disk formation models with ALMA observations

Harsono

Dishoeck

Bruderer

et al. 2015

A&A

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Context. Recent simulations have explored different ways to form accretion disks around low-mass stars. However, it has been difficult to differentiate between the proposed mechanisms because of a lack of observable predictions from these numerical studies. Aims. We aim to present observables that can differentiate a rotationally supported disk from an infalling rotating envelope toward deeply embedded young stellar objects (M env > M disk ) and infer their masses and sizes. Methods. Two 3D magnetohydrodynamics (MHD) formation simulations are studied with a rotationally supported disk (RSD) forming in one but not the other (where a pseudo-disk is formed instead), together with the 2D semi-analytical model. We determine the dust temperature structure through continuum radiative transfer RADMC3D modeling. A simple temperature-dependent CO abundance structure is adopted and synthetic spectrally resolved submm rotational molecular lines up to J u = 10 are compared with existing data to provide predictions for future ALMA observations. Results. The 3D MHD simulations and 2D semi-analytical model predict similar compact components in continuum if observed at the spatial resolutions of 0.5-1 (70-140 AU) typical of the observations to date. A spatial resolution of ∼14 AU and high dynamic range (>1000) are required in order to differentiate between RSD and pseudo-disk formation scenarios in the continuum. The first moment maps of the molecular lines show a blue-to red-shifted velocity gradient along the major axis of the flattened structure in the case of RSD formation, as expected, whereas it is along the minor axis in the case of a pseudo-disk. The peak position-velocity diagrams indicate that the pseudo-disk shows a flatter velocity profile with radius than does an RSD. On larger scales, the CO isotopolog line profiles within large (>9 ) beams are similar and are narrower than the observed line widths of low-J (2-1 and 3-2) lines, indicating significant turbulence in the large-scale envelopes. However a forming RSD can provide the observed line widths of high-J (6-5, 9-8, and 10-9) lines. Thus, either RSDs are common or a higher level of turbulence (b ∼ 0.8 km s −1 ) is required in the inner envelope compared with the outer part (0.4 km s −1 ). Conclusions. Multiple spatially and spectrally resolved molecular line observations can differentiate between the pseudo-disk and the RSD much better than continuum data. The continuum data give a better estimate of disk masses, whereas the disk sizes can be estimated from the spatially resolved molecular lines observations. The general observable trends are similar between the 2D semi-analytical models and 3D MHD RSD simulations.

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Protostellar disk formation and transport of angular momentum during magnetized core collapse

Cited by 286 publications

References 51 publications

Cosmic-ray ionisation in collapsing clouds

Cosmic-ray ionisation in collapsing clouds

Accretion and magnetic field morphology around Class 0 stage protostellar discs

Testing protostellar disk formation models with ALMA observations

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