Interstellar turbulence driven by the magnetorotational instability

Dziourkevitch, N.; Elstner, D.; Rüdiger, G.

doi:10.1051/0004-6361:200400029

Cited by 41 publications

(42 citation statements)

References 20 publications

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“…As an aside, we note that in MRI turbulence, the velocity dispersion is typically found to be linked to the Alfvén speed (Dziourkevitch et al 2004). As can be seen in Fig.…”

Section: Role Of Dynamical Instabilitiesmentioning

confidence: 75%

Towards a hybrid dynamo model for the Milky Way

Gressel¹,

Elstner²,

Ziegler³

2013

A&A

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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.

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“…As an aside, we note that in MRI turbulence, the velocity dispersion is typically found to be linked to the Alfvén speed (Dziourkevitch et al 2004). As can be seen in Fig.…”

Section: Role Of Dynamical Instabilitiesmentioning

confidence: 75%

Towards a hybrid dynamo model for the Milky Way

Gressel¹,

Elstner²,

Ziegler³

2013

A&A

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“…How a field with such a configuration, i.e., with many reversals, is formed is a question that still needs to be answered, in spite of the general opinion that a dynamo is involved. A possible clue to the source of the reversals may be the connection between the velocity profile (across pressure maxima and minima in a galactic disc) and the direction of the field, found in numerical MHD calculations by Dziourkevitch et al (2004) and Johansen et al (2009).…”

Section: Summary and Discussionmentioning

confidence: 99%

The large-scale magnetic field in the fourth Galactic quadrant

Nota¹,

Katgert²

2010

A&A

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Aims. We have re-examined the published rotation measures (RMs) of extragalactic point sources and pulsars with |b| < 3 • to study the magnetic field in the fourth Galactic quadrant. Methods. We reduced the influence of structure in electron density as much as possible by excluding objects for which Hα-data indicate large fluctuations in n e somewhere along the line of sight. We also excluded objects for which the RM may have been significantly "corrupted" by an intervening supernova remnant. We modeled RM(l), the longitude dependence of RM of the unaffected extragalactic sources and pulsars. We assumed several geometries for the large-scale field. All but one of those are based on logarithmic spiral arms (with various pitch angles and widths), while one has circular symmetry. We also made different assumptions about the large-scale n e -distribution. Results. The data suggest the following generic behaviour of the large-scale field in the 4th Galactic quadrant. The field is most likely organized along logarithmic spiral arms and shows two significant reversals: from the Norma arm (CCW field) to the Norma-Crux interarm region (CW field), and from the Norma-Crux interarm region to the Crux arm (CCW field). The present data do not constrain the field in and beyond the Crux-Carina interarm region. Although the models give a good description of the global character of RM(l), individual RM-estimates deviate by typically 15 times their measurement errors. We argue that these large deviations are most likely due to the "small-scale" field that dominates on scales of up to several hundred pc. Conclusions. The picture that emerges is thus of a field that has significant structure on smaller scales, but for which the average values in arms and interarm regions are nevertheless well-defined. In addition, this smaller-amplitude large-scale field appears to reverse at each arm-interarm boundary that we can study with the present data. We briefly discuss the link between these results and theoretical predictions.

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“…Numerical simulations geared towards the Galactic disk (e.g. Dziourkevitch et al, 2004;Piontek & Ostriker, 2004;Piontek & Ostriker, 2005) are not fully conclusive and in general deliver values ofė that are too small. Overall, the magnetorotational instability may provide a base value for the velocity dispersion below which no galaxy will fall, but it seems likely that additional processes are needed to explain the observations.…”

Section: Magnetorotational Instabilitiesmentioning

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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Interstellar turbulence driven by the magnetorotational instability

Cited by 41 publications

References 20 publications

Towards a hybrid dynamo model for the Milky Way

Towards a hybrid dynamo model for the Milky Way

The large-scale magnetic field in the fourth Galactic quadrant

Physical Processes in the Interstellar Medium

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