Detectability of Continuous Gravitational Waves from Magnetically Deformed Neutron Stars

Abstract

Neutron stars are known to contain extremely powerful magnetic fields. Their effect is to deform the shape of the star, leading to the potential emission of continuous gravitational waves. The magnetic deformation of neutron stars, however, depends on the geometry and strength of their internal magnetic field as well as on their composition, described by the equation of state. Unfortunately, both the configuration of the magnetic field and the equation of state of neutron stars are unknown, and assessing the detectability of continuous gravitational waves from neutron stars suffers from these uncertainties. Using our recent results relating the magnetic deformation of a neutron star to its mass and radius—based on models with realistic equations of state currently allowed by observational and nuclear physics constraints—and considering the Galactic pulsar population, we assess the detectability of continuous gravitational waves from pulsars in the galaxy by current and future gravitational waves detectors.

Numerical Equilibrium Configurations and Quadrupole Moments of Post-Merger Differentially Rotating Relativistic Stars

“…The slightly lower coefficient that we find in this case, can be attributed partly to the bias in the definition of the moment of inertia that we have discussed above. This however confirms that the combined use of the GR moment of inertia, for which, in the case of uniform rotators, one can adopt the quasi-universal relation in [49], together with the Newtonian deformation rate, that can be easily computed on stellar model without the need of complex asymptotic metric extrapolations, can be used as a reliable proxy for the full GR quadrupole (see the recent work [55]). Interestingly, this agrees with what found for non-rotating magnetized NSs [54].…”

Wave-optical Effects in the Microlensing of Continuous Gravitational Waves by Star Clusters

“…It is hoped that continuous GW signals from (magnetically deformed or otherwise) neutron stars may be detected in the near future. Owing to their comparatively weak strain (1), a measurement likely requires observational monitoring for at least a year with current technology (Soldateschi & Bucciantini 2021;Suvorov 2021), during which the relative motion between the source and the detector is important, especially if matched filtering is to be carried out (Jaranowski et al 1998;Dreissigacker et al 2018). Although rare, it is possible that intermittent lensing by one or more stars may take place for sources located within/behind the Galactic bulge or a globular cluster, modulating the resulting signal to a degree that depends on the GW frequency, the lens distribution, and the source velocity (Paczyński 1986b;de Paolis et al 2001;Meena & Bagla 2020).…”

“…with 90% confidence (Watts et al 2008), where S n is the noise power spectral density of the detector. Although not shown here (see, for example, Figure 5 in Soldateschi & Bucciantini 2021), it is likely that observations spanning at least a year would be necessary to detect continuous GWs from many of the known sources with existing instruments (see also Lasky 2015;Suvorov 2021). Suppose, however, that the GWs from the system were lensed en route to the detector.…”

“…Unlike in the case of a merging binary, where the bulk of the GW luminosity is produced within a few seconds, continuous GW emissions from a deformed neutron star are longer livedpotentially persisting for its entire lifetime-though much fainter; see Equation (1). With present-day (future) instruments, it is likely therefore that the detection of these sources will require monitoring for a year (month) or more (Soldateschi & Bucciantini 2021;Suvorov 2021). If the line of sight linking the neutron star to the detector intersects with a dense cluster during the observation, lensing effects may modulate the strain, as explored in Figures 6 and 9.…”

“…Although impressive advances have been made in the numerical implementation of ray-shooting codes in geometric optics (Garsden & Lewis 2010;Lewis 2020), such tools are not applicable in this case. Wave-optical lensing for continuous GWs may be especially impactful because detections would likely take many months of persistent monitoring using phasecoherent strategies (Lasky 2015;Dergachev & Papa 2021;Soldateschi & Bucciantini 2021;Suvorov 2021), and the line of sight may cross a number of interference fringes during this time.…”