The Hall effect in accretion flows

Braiding, Catherine; Wardle, Mark

doi:10.1111/j.1365-2966.2012.22001.x

Cited by 39 publications

(29 citation statements)

References 20 publications

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“…They showed that the Hall effect promotes disc formation when the magnetic field is anti-aligned with the rotation axis, while it inhibits disc formation when the field and rotation axes are aligned, confirming earlier analytic studies (e.g. Braiding & Wardle 2012). Tsukamoto et al (2015a) performed non-ideal RMHD calculations that followed the collapse until just before stellar core formation that included both Ohmic resistivity and ambipolar diffusion (but not the Hall effect).…”

Section: Introductionsupporting

confidence: 62%

The collapse of a molecular cloud core to stellar densities using radiation non-ideal magnetohydrodynamics

Wurster

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2018

Monthly Notices of the Royal Astronomical Society

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We present results from radiation non-ideal magnetohydrodynamics (MHD) calculations that follow the collapse of rotating, magnetised, molecular cloud cores to stellar densities. These are the first such calculations to include all three non-ideal effects: ambipolar diffusion, Ohmic resistivity and the Hall effect. We employ an ionisation model in which cosmic ray ionisation dominates at low temperatures and thermal ionisation takes over at high temperatures. We explore the effects of varying the cosmic ray ionisation rate from ζ cr = 10 −10 to 10 −16 s −1 . Models with ionisation rates 10 −12 s −1 produce results that are indistinguishable from ideal MHD. Decreasing the cosmic ray ionisation rate extends the lifetime of the first hydrostatic core up to a factor of two, but the lifetimes are still substantially shorter than those obtained without magnetic fields. Outflows from the first hydrostatic core phase are launched in all models, but the outflows become broader and slower as the ionisation rate is reduced. The outflow morphology following stellar core formation is complex and strongly dependent on the cosmic ray ionisation rate. Calculations with high ionisation rates quickly produce a fast (≈ 14 km s −1 ) bipolar outflow that is distinct from the first core outflow, but with the lowest ionisation rate a slower (≈ 3 − 4 km s −1 ) conical outflow develops gradually and seamlessly merges into the first core outflow.

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Section: Introductionsupporting

confidence: 62%

The collapse of a molecular cloud core to stellar densities using radiation non-ideal magnetohydrodynamics

Wurster

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2018

Monthly Notices of the Royal Astronomical Society

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“…If the interpretation of the counter rotation is correct, the effect of magnetic fields is a promising source to realize such a velocity structure. The physical mechanism to produce such a counter rotation through magnetic fields is known as the Hall effect, one of the non-ideal MHD effects (Wardle 2004;Wardle & Salmeron 2012;Braiding & Wardle 2012a;Braiding & Wardle 2012b). In collapsing cloud cores, the Hall effect induces toroidal (or azimuthal component of) magnetic fields from poloidal magnetic fields at the mid-plane of the pseudo-disk or the flattened envelope.…”

Section: Discussionmentioning

confidence: 99%

Possible Counterrotation between the Disk and Protostellar Envelope around the Class I Protostar IRAS 04169+2702

Takakuwa

Tsukamoto

Saigo

et al. 2018

ApJ

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We present results from our SMA observations and data analyses of the SMA archival data of the Class I protostar IRAS 04169+2702. The high-resolution (∼0. 5) 13 CO (3-2) image cube shows a compact (r 100 au) structure with a northwest (blue) to southeast (red) velocity gradient, centered on the 0.9-mm dust-continuum emission. The direction of the velocity gradient is orthogonal to the axis of the molecular outflow as seen in the SMA 12 CO (2-1) data. A similar gas component is seen in the SO (6 5 -5 4 ) line. On the other hand, the C 18 O (2-1) emission traces a more extended (r ∼400 au) component with the opposite, northwest (red) to southeast (blue) velocity gradient. Such opposite velocity gradients in the different molecular lines are also confirmed from direct fitting to the visibility data. We have constructed models of a forward-rotating and counter-rotating Keplerian disk and a protostellar envelope, including the SMA imaging simulations. The counter-rotating model could better reproduce the observed velocity channel maps, although we could not obtain statistically significant fitting results. The derived model parameters are; Keplerian radius of 200 au, central stellar mass of 0.1 M , and envelope rotational and infalling velocities of 0.20 km s −1 and 0.16 km s −1 , respectively. One possible interpretation for these results is the effect of the magnetic field in the process of disk formation around protostars, i.e., Hall effect.

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“…Ambipolar diffusion and Ohmic resistivity lead to the diffusion of gas relative to the magnetic field and, therefore, are likely to lead to weaker fossil magnetic fields. The Hall effect is not diffusive but modifies the geometry of the magnetic field to increase or decrease the angular momentum in the dense gas that collapses to the equatorial plane (Braiding & Wardle 2012). Recent star formation studies have included some or all of these non-ideal effects (e.g.…”

Section: Introductionmentioning

confidence: 99%

On the origin of magnetic fields in stars

Wurster

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2018

Monthly Notices of the Royal Astronomical Society

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Are the kG-strength magnetic fields observed in young stars a fossil field left over from their formation or are they generated by a dynamo? We use radiation non-ideal magnetohydrodynamics simulations of the gravitational collapse of a rotating, magnetized molecular cloud core over 17 orders of magnitude in density, past the first hydrostatic core to the formation of the second, stellar core, to examine the fossil field hypothesis. Whereas in previous work we found that magnetic fields in excess of 10 kG can be implanted in stars at birth, this assumed ideal magnetohydrodynamics (MHD), i.e. that the gas is coupled to the magnetic field. Here we present non-ideal MHD calculations which include Ohmic resistivity, ambipolar diffusion and the Hall effect. For realistic cosmic ray ionization rates, we find that magnetic field strengths of kG are implanted in the stellar core at birth, ruling out a strong fossil field. While these results remain sensitive to resolution, they cautiously provide evidence against a fossil field origin for stellar magnetic fields, suggesting instead that magnetic fields in stars originate in a dynamo process.

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The Hall effect in accretion flows

Cited by 39 publications

References 20 publications

The collapse of a molecular cloud core to stellar densities using radiation non-ideal magnetohydrodynamics

The collapse of a molecular cloud core to stellar densities using radiation non-ideal magnetohydrodynamics

Possible Counterrotation between the Disk and Protostellar Envelope around the Class I Protostar IRAS 04169+2702

On the origin of magnetic fields in stars

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