Scientific Seminars

The magnetars as a consequence of magnetic field amplification by dynamo effect

L. Paterno'
Department of Physics and Astronomy, University of Catania

2009-05-26    11.30    Merate - POE

The magnetars (magnetic stars) are neutron stars with huge magnetic fields of the order of 10^14 - 10^15 Gauss that show soft gamma and X emission. Only 16 magnetars have been discovered until now, 3 of which to be confirmed, all located in a range between about 3 kpc and 50 kpc. The unusual strength of their magnetic fields cannot simply be explained in terms of a primordial magnetic field amplified during the collapse of the neutron star owing to the conservation of magnetic flux. Some further amplification can take place during the ∼ 40s transition phase from a proto-neutron star to a neutron star by means of a dynamo mechanism able to intensify the magnetic field to exceed by orders of magnitude the energy equipartition value. During the transition phase a hydrodynamic instability arises, called neutron finger instability, in the upper layers of the star caused by the large lepton gradient. The non-uniform rotation created by this turbulent instability permits the dynamo action. We used a proto-neutron star model, solved the relevant non-linear partial differential equations in a simplified geometry, and demonstrated that magnetic fields of the order of those observed in magnetars can easily be obtained.