On magnetic instabilities and dynamo action in stellar radiation zones

By J. Zahn, A. Brun, S. Luth, O. Paris, Meudon, France., S. d’Astrophysique, C. Saclay, Gif-sur-Yvette, Observatoire de Geneve and 2 more. 2007

208 citations recorded by the source corpus.

Context. We examine the MHD instabilities arising in the radiation zone of a differentially rotating star, in which a poloidal field of fossil origin is sheared into a toroidal field. Aims. We focus on the non-axisymmetric instability that affects the toroidal magnetic field in a rotating star, which was first studied by Pitts and Tayler in the non-dissipative limit. If such an instability were able to mix the stellar material, it could have an impact on the evolution of the star. According to Spruit, it could also drive a dynamo. Methods. We compare the numerical solutions built with the 3-dimensional ASH code with the predictions drawn from an analytical study of the Pitts & Tayler instability. Results. The Pitts & Tayler instability is manifestly present in our simulations, with its conspicuous m = 1 dependence in azimuth. But its analytic treatment used so far is too simplified to be applied to the real stellar situation. Although the instability generated field reaches an energy comparable to that of the mean poloidal field, that field seems unaffected by the instability: it undergoes Ohmic decline, and is neither eroded nor regenerated by the instability. The toroidal field is produced by shearing the poloidal field and it draws its energy from the differential rotation. The small scale motions behave as Alfven waves; they cause negligible eddy-diffusivity and contribute little to the net transport of angular momentum. Conclusions. In our simulations we observe no sign of dynamo action, of either mean field or fluctuation type, up to a magnetic Reynolds number of 10 5 . However the Pitts & Tayler instability is sustained as long as the differential rotation acting on the poloidal field is able to generate a toroidal field of sufficient strength. But in the Sun such a poloidal field of fossil origin is ruled out by the nearly uniform rotation of the deep interior.

Subfields: Astronomy and Astrophysics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/f9f17e3639a3f5f9c531d8e3e825c2cae9cc1f78

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In Astronomy and Astrophysics

1. N. Langer
2. Selma de Mink
3. J. Fuller
4. Aaron Dotter
5. G. Meynet
6. Matteo Cantiello
7. C. Conroy
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In Molecular Biology

1. J. Christensen-Dalsgaard
2. J. Fuller
3. A. Piro

Citations in the corpus

• ANGULAR MOMENTUM TRANSPORT WITHIN EVOLVED LOW-MASS STARS (2014, background): “While the physics of the Tayler instability is secure, the existence of the Tayler-Spruit dynamo loop is debated on both analytical and numerical grounds (Braithwaite 2006; Zahn et al. 2007).”
• Slowing the spins of stellar cores (2019, methodology): “…485, 3661–3680 (2019) D ow nloaded from https://academ ic.oup.com /m nras/article-abstract/485/3/3661/5347954 by C alifornia Institute of Technology user on 25 April 2019 by Zahn et al. (2007) that winding of the non-axisymmetric field cannot regenerate the axisymmetric toroidal field.”
• Grids of stellar models with rotation - II. WR populations and supernovae/GRB progenitors at Z = 0.014 (2012, background): “Third, some authors (Zahn et al. 2007) have challenged the shear dynamo theory presently adopted in the models responsible for the strong coupling.”
• Angular momentum transport by heat-driven g-modes in slowly pulsating B stars (2017, methodology): “The efficacy of the TS dynamo remains a topic of ongoing debate (see, e.g., Spruit 2002; Denissenkov & Pinsonneault 2007; Zahn et al. 2007), and we therefore perform two simulations: for our ‘magnetic’ simulation the dynamo is enabled in mesastar, and for the ‘non-magnetic’ one it is turned off.”
• MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): PLANETS, OSCILLATIONS, ROTATION, AND MASSIVE STARS (2013, background): “Such a dynamo process has been proposed by Spruit (2002, Spruit-Tayler dynamo); a theoretical debate on this is still ongoing (Braithwaite 2006; Zahn et al. 2007; Denissenkov & Pinsonneault 2007).”
• Effects of rotation on the evolution of primordial stars (2008, background): “For instance, Zahn et al. (2007) have shown that although the Pitts and Tayler instability indeed develops, it does not succeed in driving a dynamo.”
• Rotating massive main-sequence stars - I. Grids of evolutionary models and isochrones (2011, background): “We note that, while the dynamo process itself was confirmed through numerical calculations by Braithwaite (2006), it is still unclear under which conditions it can operate and whether it is active in massive stars (Zahn et al. 2007).”
• MESA ISOCHRONES AND STELLAR TRACKS (MIST). I. SOLAR-SCALED MODELS (2016, background): “We note that the very existence of the ST-dynamo loop is still under debate (Braithwaite 2006; Zahn et al. 2007), and there are ongoing efforts to understand the role of angular momentum transport via magnetic fields in radiative stellar regions (e.g. Rüdiger et al. 2015; Wheeler et al. 2015).”