Magnetic fields generated by r-modes in accreting quark stars

L. Bonanno^1,3, C. Cuofano², A. Drago², G. Pagliara¹ and J. Schaffner-Bielich¹

¹ Institut für Theoretische Physik, Ruprecht-Karls-Universität, Philosophenweg 16, 69120 Heidelberg, Germany
e-mail: bonanno@fe.infn.it
² Dipartimento di Fisica, Universitá di Ferrara and INFN sezione di Ferrara, 44100 Ferrara, Italy
³ Institute for Theoretical Physics, Goethe University, Max-von-Laue-Str. 1, 60438 Frankfurt am Main, Germany

Received: 4 February 2011
Accepted: 29 May 2011

Abstract

We show that the r-mode instability can generate strong toroidal fields in the core of accreting millisecond quark stars by inducing differential rotation. We follow the spin frequency evolution on a long time-scale, taking into account the magnetic damping rate in the evolution equations of r-modes. The maximum spin frequency of the star is only marginally lower than without the magnetic field. The late-time evolution of the stars that enter the r-mode instability region is instead quite different if the generated magnetic fields are taken into account: they leave the millisecond pulsar region and become radio pulsars.