Hall effect and differential rotation in protoneutron stars

• Antragsteller: Professor Dr. Günther Rüdiger
• Fachliche Zuordnung: Astrophysik und Astronomie
• Förderung: Förderung von 2008 bis 2013
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 61662977

Collapse calculations lead to the result that the hot newly born protoneutron stars (PNS) rotate differentially. Due to their extraordinary strong magnetic fields also the Hall effect appears to be important for PNS. Differential rotation and Hall effect together are known to produce the shear-Hall instability (SHI) if the shear is strong enough and the Hall parameter Rb = wBr is of order unity. The latter is realized only for very hot young neutron stars. If the neutron star cools down, the Hall parameter grows and the system is stabilized.An important characteristic of the SHI is its distinct dependence on the sign of the magnetic field. The SHI only works for magnetic fields parallel to the rotation axis. In the opposite case the magnetorotational instability (MRI) works but under modification by the Hall effect.It is proposed to study this exciting situation in order to attack the question whether in the nonlinear case the SHI can act as a dynamo and if YES with which amplitude. We have already found the excitation conditions for such a completely new nonlinear and nonturbulent dynamo type whose importance for astrophysical objects (such as neutron stars) must be checked.The induced toroidal magnetic fields can only reach amplitudes which are stable with respect to the Tayler (or pinch-type) instability. On the other hand the lifetime of differential rotation is restricted by the magnetic-induced angular momentum transport. This backreaction of the dynamo onto the differential rotation is thus a basic open question which limits the lifetime of the dynamo regime and also the amplitude of the excited magnetic fields.

• DFG-Verfahren: Sachbeihilfen
• Internationaler Bezug: Chile
• Beteiligte Personen: Dr. Rainer Arlt; Professor Dr. Andreas Reisenegger