Continuous gravitational waves and magnetic monopole signatures from single neutron stars

Abstract

Future observations of continuous gravitational waves from single neutron stars, apart from their monumental astrophysical significance, could also shed light on fundamental physics and exotic particle states. One such avenue is based on the fact that magnetic fields cause deformations of a neutron star, which results in a magnetic-field-induced quadrupole ellipticity. If the magnetic and rotation axes are different, this quadrupole ellipticity may generate continuous gravitational waves which may last decades, and may be observable in current or future detectors. Light, milli-magnetic monopoles, if they exist, could be pair-produced non-perturbatively in the extreme magnetic fields of neutron stars, such as magnetars. This non-perturbative production furnishes a new, direct dissipative mechanism for the neutron star magnetic fields. Through their consequent effect on the magnetic-fieldinduced quadrupole ellipticity, they may then potentially leave imprints in the early stage continuous gravitational wave emissions. We speculate on this possibility in the present study, by considering some of the relevant physics and taking a very simplified toy model of a magnetar as the prototypical system. Preliminary indications are that new-born millisecond magnetars could be promising candidates to look for such imprints. Deviations from conventional evolution, and comparatively abrupt features in the early stage gravitational waveforms, distinct from other astrophysical contributions, could be distinguishable signatures for these exotic monopole states.

The impact of superconductivity and the Hall effect in models of magnetised neutron stars

“…Finally, let us discuss the magnetic deformation of the star, which plays an important role in estimating the strength of gravitational radiation from NSs (Ushomirsky et al 2000;Haskell et al 2008;Mastrano et al 2013;Lasky 2015;Gao et al 2017;Sieniawska & Table 1.The percentage of E tor /E mag for different parameter values of s for n 2 (r) = (1 − r 2 ). A comparison is also shown with Armaza et al (2015) and Gourgouliatos et al (2013 Bejger 2019; Chandra et al 2020). In our setup, as already discussed, this can be treated as a higher order effect in an expansion in O(B 2 ).…”

Magnetic fields in compact stars and related phenomena

“…Even though our common sense could suggest that magnetized compact objects become prolate (with respect to the magnetic field axis) due to the axial symmetry imposed in the system by the magnetic field [146,147], for the typical values of the magnetic field and density here analyzed for white dwarfs and neutron star models, the Maxwell pressures dominate, making P T < P T ⊥ and resulting in oblate COs. Nowadays, with the detection of gravitational waves, a new window is open for more accurate measurements of the properties of neutron stars. As both magnetic fields and rotation deform isolated neutron stars, they should leave fingerprints in the gravitational wave signals coming from these objects [148][149][150]. Therefore, the measurement in the future of these signals might allow unveiling the fundamental properties of exotic particle states inside the magnetized neutron stars.…”

The impact of superconductivity and the Hall effect in models of magnetized neutron stars

“…Finally, let us discuss the magnetic deformation of the star, which plays an important role in estimating the strength of gravitational radiation from NSs (Ushomirsky et al, 2000;Haskell et al, 2008;Mastrano et al, 2013;Lasky, 2015;Gao et al, 2017;Sieniawska & Bejger, 2019;Chandra et al, 2020). In our setup, as already discussed, this can be treated as a higher order effect in an expansion in O(B 2 ).…”