Magnetic fields generated by r-modes in accreting quark stars

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.

Generation of strong magnetic fields byr-modes in millisecond accreting neutron stars: Induced deformations and gravitational wave emission

“…In this type of stars the viscosity and thus the r-mode instability window is quite different from that of normal NSs [32]. Moreover, the evolution of the internal magnetic fields and the magnetic properties of the compact star are also expected to be different [8,33].…”

“…[1][2][3]6] and in the case of accreting millisecond neutron and quark stars in Refs. [7,8]. Magnetic fields deform the star and if the magnetic axis is not aligned with the rotation axis the NS undergoes free body precession.…”

Growth of magnetic fields in accreting millisecond pulsars

“…We have discussed the evolution of the external magnetic field of recycled MSPs due to the diffusion of strong internal magnetic fields generated by r-modes during the mass accretion phase. Our analysis is based on the previous work of Cuofano & Drago (2010) and Bonanno et al (2011) where it has been shown that r-modes generate strong internal magnetic fields in accreting compact stars. We have shown that the growth of the external magnetic field affects the evolution of the spin-down rate Ṗ of the MSPs and that this mechanism can explain the high Ṗ of J1823-3021A and of J1824-2452A.…”

“…In recent papers it has been proposed a mechanism based on the r-mode instability for the evolution of the internal magnetic field in millisecond accreting compact stars (Cuofano & Drago 2010;Bonanno et al 2011;Cuofano et al 2012). R-modes represent a class of oscillation modes in rotating neutron stars, which are unstable with respect to the emission of gravitational waves (Andersson & Kokkotas 2001).…”

An r-mode in a magnetic rotating spherical layer: application to neutron stars

“…Ho & Lai 2000). More recently, Cuofano & Drago (2010) and Bonanno et al (2011) investigated the role of magnetic field generation by the unstable r ‐mode, showing that a very strong toroidal magnetic field can be generated, which can, in turn, modify the instability.…”