On the origin of magnetic fields in stars

Wurster, James; Bate, Matthew R.; Price, Daniel J.

doi:10.1093/mnras/sty2438

Cited by 30 publications

(25 citation statements)

References 63 publications

(86 reference statements)

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“…Star formation begins later in the high resolution models, with higher-resolution models collapsing slower than their lowerresolution counterparts (as previously discussed in Wurster et al 2018c). Once the star formation begins in I05 h , the star formation rate is similar to that of I05, and both models have accelerating star formation rates.…”

Section: A2 Stellar Populationsmentioning

confidence: 64%

There is no magnetic braking catastrophe: low-mass star cluster and protostellar disc formation with non-ideal magnetohydrodynamics

Wurster

Bate

Price

2019

Monthly Notices of the Royal Astronomical Society

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We present results from the first radiation non-ideal magnetohydrodynamics (MHD) simulations of low-mass star cluster formation that resolve the fragmentation process down to the opacity limit. We model 50 M turbulent clouds initially threaded by a uniform magnetic field with strengths of 3, 5 10 and 20 times the critical mass-to-magnetic flux ratio, and at each strength, we model both an ideal and non-ideal (including Ohmic resistivity, ambipolar diffusion and the Hall effect) MHD cloud. Turbulence and magnetic fields shape the large-scale structure of the cloud, and similar structures form regardless of whether ideal or non-ideal MHD is employed. At high densities (10 6 n H 10 11 cm −3 ), all models have a similar magnetic field strength versus density relation, suggesting that the field strength in dense cores is independent of the large-scale environment. Albeit with limited statistics, we find no evidence for the dependence of the initial mass function on the initial magnetic field strength, however, the star formation rate decreases for models with increasing initial field strengths; the exception is the strongest field case where collapse occurs primarily along field lines. Protostellar discs with radii 20 au form in all models, suggesting that disc formation is dependent on the gas turbulence rather than on magnetic field strength. We find no evidence for the magnetic braking catastrophe, and find that magnetic fields do not hinder the formation of protostellar discs.

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Section: A2 Stellar Populationsmentioning

confidence: 64%

There is no magnetic braking catastrophe: low-mass star cluster and protostellar disc formation with non-ideal magnetohydrodynamics

Wurster

Bate

Price

2019

Monthly Notices of the Royal Astronomical Society

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“…The cloud evolution during the gas collapsing phase was investigated in many past studies (e.g. Banerjee & Pudritz 2006;Machida et al 2006;Tomida et al 2015;Tsukamoto et al 2015;Wurster et al 2018). At first, we overview the driving of outflows in the accreting cloud.…”

Section: Resultsmentioning

confidence: 99%

Origin of misalignments: protostellar jet, outflow, circumstellar disc, and magnetic field

Hirano

Machida

2019

Monthly Notices of the Royal Astronomical Society

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Recent observations uncover various phenomena around the protostar such as misalignment between the outflow and magnetic field, precession of the jet, and time variability of the ejected clumps, whose origins are under debate. We perform a three-dimensional resistive magnetohydrodynamics simulation of the protostar formation in a star-forming core whose rotation axis is tilted at an angle 45 • with respect to the initial magnetic field, in which the protostar is resolved with a spatial resolution of 0.01 au. In low-dense outer region, the prestellar core contracts along the magnetic field lines due to the flux freezing. In high-dense inner region, on the other hand, the magnetic dissipation becomes efficient and weakens the magnetic effects when the gas number density exceeds about 10 11 cm −3 . Then, the normal direction of the flattened disc is aligned with the angular momentum vector. The outflow, jet, and protostellar ejection are driven from different scales of the circumstellar disc and spout in different directions normal to the warped disc. These axes do not coincide with the global magnetic field direction and vary with time. This study demonstrates that a couple of misalignment natures reported by observations can be simultaneously reproduced only by assuming the star-forming core rotating around a different direction from the magnetic field.

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“…In ideal magnetohydrodynamics (MHD) studies of the formation of an isolated star, magnetic fields of 10 4 − 10 6 G are shown to be implanted in the stellar core at birth (e.g. Machida et al 2006Machida et al , 2007Bate et al 2014;Wurster et al 2018d;Vaytet et al 2018). This magnetic field was much stronger than expected, and largely resulted because ideal MHD was employed.…”

Section: Introductionmentioning

confidence: 99%

“…Many studies, however, perform their simulations at various resolutions to understand how resolution affects their results (e.g. Schmidt et al 2010;Federrath 2015;Wurster et al 2016Wurster et al , 2018dCunningham et al 2018;Grudić et al 2021), while several have shown that their results remain unconverged, even when using the highest resolution feasible (e.g. Mac Low et al 1998;Meru & Bate 2011;Joos et al 2013;Bate et al 2014;Hosokawa et al 2016;Haugbølle et al 2018;Meyer et al 2018;Hennebelle 2018), and a few have shown that convergence has been reached (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Increasing numerical resolution tends to increase the magnetic field strength in a newly formed protostar (e.g. Bate et al 2014;Wurster et al 2018d) since the protostar is better resolved and its properties (including gas density and magnetic field strength) suffer less smoothing. Therefore, the question arises as to whether or not the conclusions of Paper I will hold at even higher resolutions.…”

Section: Introductionmentioning

confidence: 99%

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On the origin of magnetic fields in stars – II. The effect of numerical resolution

Wurster

Bate

Price

et al. 2022

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? Our previous numerical study concluded that magnetic fields must originate by a dynamo process. Here, we continue that investigation by performing even higher numerical resolution calculations of the gravitational collapse of a 1 M⊙ rotating, magnetised molecular cloud core through the first and second collapse phases until stellar densities are reached. Each model includes Ohmic resistivity, ambipolar diffusion, and the Hall effect. We test six numerical resolutions, using between 105 and 3 × 107 particles to model the cloud. At all but the lowest resolutions, magnetic walls form in the outer parts of the first hydrostatic core, with the maximum magnetic field strength located within the wall rather than at the centre of the core. At high resolution, this magnetic wall is disrupted by the Hall effect, producing a magnetic field with a spiral-shaped distribution of intensity. As the second collapse occurs, this field is dragged inward and grows in strength, with the maximum field strength increasing with resolution. As the second core forms, the maximum field strength exceeds 1 kG in our highest resolution simulations, and the stellar core field strength exceeds this threshold at the highest resolution. Our resolution study suggests that kG-strength magnetic fields may be implanted in low-mass stars during their formation, and may persist over long timescales given that the diffusion timescale for the magnetic field exceeds the age of the Universe.

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On the origin of magnetic fields in stars

Cited by 30 publications

References 63 publications

There is no magnetic braking catastrophe: low-mass star cluster and protostellar disc formation with non-ideal magnetohydrodynamics

There is no magnetic braking catastrophe: low-mass star cluster and protostellar disc formation with non-ideal magnetohydrodynamics

Origin of misalignments: protostellar jet, outflow, circumstellar disc, and magnetic field

On the origin of magnetic fields in stars – II. The effect of numerical resolution

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