École Nationale Supérieure de
Techniques Avancées

Résumé

The magnetorotational instability (MRI) is considered to be a promising mechanism to amplify the magnetic field in fast-rotating protoneutron stars. Many local studies have proven that the magnetic field could be amplified on small scales. But to explain the dipolar magnetic field strength of the magnetars (10^14 − 10^15 G), a large scale magnetic field needs to be generated by the MRI. To study this question, a three dimensional pseudo-spectral code has been used to develop a global model of the MRI in a proto-neutron star. The hypotheses of an incompressible fluid and a constant density allow us to simplify at maximum the model. A new boundary condition is implemented to obtain a quasi-stationnary state of the MRI. We find on average a lower turbulence in the global model than local simulations due to the geometry of the domain. We also show that a strength of the dipolar magnetic field consistent with the values of magnetar’s strong fields can be generated by the MRI, even though it is lower than the small scale magnetic field. Overall, the results presented in this report support the ability of the MRI to form magnetar-like large scale magnetic fields.