Seed fields for galactic dynamos   by the magnetorotational instability

Kitchatinov, L. L.; Rüdiger, G.

doi:10.1051/0004-6361:20040431

Cited by 36 publications

(47 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This may be because the initial magnetic field is comparatively weak and accordingly the unstable modes lie close to the diffusive border of the unstable region. In this case, the unstable mode is characterised by a dominant toroidal field (Kitchatinov & Rüdiger 2004). The pitch angle is larger for model N3d-VF with the stronger initial field of 0.1 μG, however.…”

Section: Magnetic Pitch Anglementioning

confidence: 87%

“…Prior to the epoch of star formation, the MRI may grow unhindered by turbulence from SNe and hence serve as a seed-field mechanism, as suggested by Kitchatinov & Rüdiger (2004).…”

Section: Vertical Parity and Growth Ratesmentioning

confidence: 99%

“…According to the local criterion derived in Appendix A of Kitchatinov & Rüdiger (2004), who studied the linear stability of MRI in a global cylindrical disc of semi-thickness H, instability is obtained within a range 2 − s s…”

Section: Role Of Dynamical Instabilitiesmentioning

confidence: 99%

See 2 more Smart Citations

Towards a hybrid dynamo model for the Milky Way

Gressel¹,

Elstner²,

Ziegler³

2013

A&A

View full text Add to dashboard Cite

Context. Based on the rapidly increasing all-sky data of Faraday rotation measures and polarised synchrotron radiation, the Milky Way's magnetic field can now be modelled with an unprecedented level of detail and complexity. Aims. We aim to complement this phenomenological approach with a physically motivated, quantitative dynamo model -a model that moreover allows for the evolution of the system as a whole, instead of just solving the induction equation for a fixed static disc. Methods. Building on the framework of mean-field magnetohydrodynamics and extending it to the realm of a hybrid evolution, we performed three-dimensional global simulations of the Galactic disc. To eliminate free parameters, closure coefficients embodying the mean-field dynamo were calibrated against resolved local simulations of supernova-driven interstellar turbulence. Results. The emerging dynamo solutions comprise a mixture of the dominant axisymmetric S0 mode with even parity, and a subdominant A0 mode with odd parity. Notably, this superposition of modes creates a strong localised vertical field on one side of the Galactic disc. Moreover, we found significant radial pitch angles that decay with radius, which can be explained by flaring of the disc. In accordance with previous work, magnetic instabilities appear to be restricted to the calmer outer Galactic disc. Their main effect is to create strong fields at large radii such that the radial scale length of the magnetic field increases from 4 kpc (for a mean-field dynamo alone) to about 10 kpc in the hybrid models -the latter being in much better agreement with observations. Conclusions. There remain aspects (e.g., spiral arms, X-shaped halo fields, fluctuating fields) that are not captured by the current model and that will require further development towards a fully dynamical evolution. Nevertheless, we demonstrate that a hybrid modelling of the Galactic dynamo is feasible and can serve as a foundation for future efforts.

show abstract

Section: Magnetic Pitch Anglementioning

confidence: 87%

“…Prior to the epoch of star formation, the MRI may grow unhindered by turbulence from SNe and hence serve as a seed-field mechanism, as suggested by Kitchatinov & Rüdiger (2004).…”

Section: Vertical Parity and Growth Ratesmentioning

confidence: 99%

See 1 more Smart Citation

Towards a hybrid dynamo model for the Milky Way

Gressel¹,

Elstner²,

Ziegler³

2013

A&A

View full text Add to dashboard Cite

show abstract

“…Rm 2 = Pm + S 2 2 3S 2 − 1 (9) (Kitchatinov & Rüdiger 2004). The dimensionless quantities (7) have been redefined in terms of the wave number (H → k −1 ).…”

Section: Local Analysis For Axisymmetric Modesmentioning

confidence: 99%

“…Because the pitch-angle of unstable disturbances near B min is small, the winding is strong (Kitchatinov & Rüdiger 2004). The differential rotation converts the azimuthal inhomogeneity of the nonaxisymmetric modes into a fine radial structure, which is finally destroyed by diffusion.…”

Section: Small Pmmentioning

confidence: 99%

Nonaxisymmetric modes of MRI in dissipative Keplerian disks

Kitchatinov

Rüdiger

2010

A&A

Self Cite

View full text Add to dashboard Cite

Aims. Deviations from the axial symmetry are necessary to maintain self-sustained MRI-turbulence by a dynamo mechanism. We define the parameter region where the nonaxisymmetric MRI modes are excited and study their geometries and growth rates. Methods. The linear eigenvalue problem for global nonaxisymmetric modes of standard-MRI in Keplerian disks is solved numerically with allowance for finite diffusion. Results. For small magnetic Prandtl numbers the microscopic viscosity completely drops out of the analysis so that the stability maps and the growth rates expressed in terms of the magnetic Reynolds number Rm and the Lundquist number S do not depend on the magnetic Prandtl number Pm. The minimum magnetic field for the onset of nonaxisymmetric MRI grows with the rotation rate. For a given S all nonaxisymmetric modes disappear for a sufficiently large Rm. This is a consequence of the radial fine-structure of the nonaxisymmetric modes resulting from the winding effect of differential rotation. It is this fine-structure which also provides serious resolution problems for the numerical simulation of MRI at large Rm. Conclusions. For weak magnetic fields slightly above the critical value for the onset of MRI only axisymmetric modes are unstable. Nonaxisymmetric modes need stronger fields and not too large Rm. If Pm is small its real value does not play any role in MRI.

show abstract

References

2013

Magnetic Processes in Astrophysics

View full text Add to dashboard Cite

Seed fields for galactic dynamos by the magnetorotational instability

Cited by 36 publications

References 24 publications

Towards a hybrid dynamo model for the Milky Way

Towards a hybrid dynamo model for the Milky Way

Nonaxisymmetric modes of MRI in dissipative Keplerian disks

References

Contact Info

Product

Resources

About