The effect of magnetic fields on the formation of circumstellar discs around young stars

Price, Daniel J.; Bate, Matthew R.

doi:10.1007/s10509-007-9549-x

Cited by 47 publications

(47 citation statements)

References 21 publications

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“…They found that the formation of a RSD is suppressed as long as λ is of order 5 or less. However, the λ = 5 case in Price & Bate's (2007) SPMHD simulations appears to have formed a small disk (judging from the column density distribution). It is unclear whether the disk is rotationally supported or not, since the disk rotation rate was not given in the paper.…”

Section: Magnetic Braking Catastrophe In Ideal Mhd Limitmentioning

confidence: 98%

“…Misalignment between the magnetic field and rotation axis as a way to form large RSDs has been explored extensively by Hennebelle and collaborators (Hennebelle & Ciardi 2009;Ciardi & Hennebelle 2010;Joos et al 2012; see also Machida et al 2006;Bate 2007, andKeiser 2013). The misalignment is expected if the angular momenta of dense cores are generated through turbulent motions (e.g., Burkert & Bodenheimer 2000;Seifried et al 2012b;Myers et al 2013;Joos et al 2013).…”

Section: Magnetic Field-rotation Misalignmentmentioning

confidence: 99%

See 1 more Smart Citation

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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Section: Magnetic Braking Catastrophe In Ideal Mhd Limitmentioning

confidence: 98%

Section: Magnetic Field-rotation Misalignmentmentioning

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

View full text Add to dashboard Cite

show abstract

“…Recent numerical simulations have shown that even a weak magnetic field can have noticeable dynamical effects. It can alter how cores fragment (Price & Bate, 2007bHennebelle & Fromang, 2008;Hennebelle & Teyssier, 2008;Peters et al, 2011), change the coupling between stellar feedback processes and their parent clouds (Nakamura & Li, 2007;Krumholz et al, 2007b), influence the properties of protostellar disks due to magnetic braking (Price & Bate, 2007a;Mellon & Li, 2009;Hennebelle & Ciardi, 2009;Seifried et al, , 2012aSeifried et al, ,b, 2013, or slow down the overall evolution (Heitsch et al, 2001a).…”

Section: Magnetic Field Structurementioning

confidence: 99%

Physical Processes in the Interstellar Medium

Klessen

Glover

2015

Saas-Fee Advanced Course

170

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Interstellar space is filled with a dilute mixture of charged particles, atoms, molecules and dust grains, called the interstellar medium (ISM). Understanding its physical properties and dynamical behavior is of pivotal importance to many areas of astronomy and astrophysics. Galaxy formation and evolution, the formation of stars, cosmic nucleosynthesis, the origin of large complex, prebiotic molecules and the abundance, structure and growth of dust grains which constitute the fundamental building blocks of planets, all these processes are intimately coupled to the physics of the interstellar medium. However, despite its importance, its structure and evolution is still not fully understood. Observations reveal that the interstellar medium is highly turbulent, consists of different chemical phases, and is characterized by complex structure on all resolvable spatial and temporal scales. Our current numerical and theoretical models describe it as a strongly coupled system that is far from equilibrium and where the different components are intricately linked together by complex feedback loops. Describing the interstellar medium is truly a multi-scale and multi-physics problem. In these lecture notes we introduce the microphysics necessary to better understand the interstellar medium. We review the relations between large-scale and small-scale dynamics, we consider turbulence as one of the key drivers of galactic evolution, and we review the physical processes that lead to the formation of dense molecular clouds and that govern stellar birth in their interior.

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“…The simplified framework of the ideal magnetohydrodynamics (MHD) used in the first studies led to the disappearance of the large Keplerian disks that are easily formed in hydrodynamical simulations as a result of the very effective magnetic braking created by a strong pile-up of magnetic flux towards the centre of the collapsing system (Galli et al 2006;Allen et al 2003, Price & Bate 2007Hennebelle & Teyssier 2008;Matsumoto & Tomisaka 2004;Hennebelle & Fromang 2008;Commerçon et al 2010). In these simulations, disks were found to form only for unrealistically weak magnetic field intensities (corresponding to a mass-to-flux ratio more than 10 times the critical value derived by Mouschovias & Spitzer 1976).…”

Section: Introductionmentioning

confidence: 99%

Ambipolar diffusion in low-mass star formation

Masson

Chabrier

Hennebelle

et al. 2016

A&A

206

275

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Angular momentum transport and the formation of rotationally supported structures are major issues in our understanding of protostellar core formation. Whereas purely hydrodynamical simulations lead to large Keplerian disks, ideal magnetohydrodynamics (MHD) models yield the opposite result, with essentially no disk formation. This stems from the flux-freezing condition in ideal MHD, which leads to strong magnetic braking. In this paper, we provide a more accurate description of the evolution of the magnetic flux redistribution by including resistive terms in the MHD equations. We focus more particularly on the effect of ambipolar diffusion on the properties of the first Larson core and its surrounding structure, exploring various initial magnetisations and magnetic field versus rotation axis orientations of a 1 M collapsing prestellar dense core. We used the non-ideal magnetohydrodynamics version of the adaptive mesh refinement code RAMSES to carry out these calculations. The resistivities required to calculate the ambipolar diffusion terms were computed using a reduced chemical network of charged, neutral, and grain species. Including ambipolar diffusion leads to the formation of a magnetic diffusion barrier (also known as the decoupling stage) in the vicinity of the core, which prevents accumulation of magnetic flux in and around the core and amplification of the field above 0.1 G. The mass and radius of the first Larson core, however, remain similar between ideal and non-ideal MHD models. This diffusion plateau, preventing further amplification of the field and reorganising the field topology, has crucial consequences for magnetic braking processes, allowing the formation of disk structures. Magnetically supported outflows launched in ideal MHD models are weakened or even disappear when using non-ideal MHD. In contrast to ideal MHD calculations, misalignment between the initial rotation axis and the magnetic field direction does not significantly affect the results for a given magnetisation, showing that the physical dissipation processes truly dominate numerical diffusion. We demonstrate severe limits of the ideal MHD formalism; it yields unphysical behaviours in the long-term evolution of the system. This includes counter-rotation inside the outflow or magnetic tower, interchange instabilities, and flux redistribution triggered by numerical diffusion. These effects are not observed in non-ideal MHD. Disks with Keplerian velocity profiles are found to form around the protostar in all our non-ideal MHD simulations, with a final mass and size that strongly depend on the initial magnetisation. This ranges from a few 10 −2 M and ∼20−30 au for the most magnetised case (µ = 2) to ∼2 × 10 −1 M and ∼40−80 au for a lower magnetisation (µ = 5). In all cases, these disks remain significantly smaller than disks found in pure hydrodynamical simulations. Ambipolar diffusion thus bears a crucial impact on the regulation of magnetic flux and angular momentum transport during the collapse of a prestellar core and the...

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The effect of magnetic fields on the formation of circumstellar discs around young stars

Cited by 47 publications

References 21 publications

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

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

Physical Processes in the Interstellar Medium

Ambipolar diffusion in low-mass star formation

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