Superradiant and dynamical spin-down of neutron stars with gravitational wave implications

TL;DR

This paper proposes superradiant spin-down as a new mechanism to explain anomalous neutron star spin variations and discusses associated gravitational wave signals as potential multimessenger probes.

Contribution

It introduces superradiant spin-down as a novel explanation for neutron star spin anomalies and explores gravitational wave signatures from various neutron star phenomena.

Findings

Superradiant spin-down can account for sudden enhanced spin-down events.

Gravitational wave signals from quadrupole deformation, r-mode oscillations, and axion clouds are promising multimessenger probes.

Modeling shows interplay between conventional and superradiant spin-down affects neutron star evolution.

Abstract

Neutron stars such as pulsars and magnetars lose angular momentum primarily through electromagnetic dipole radiation, gravitational waves, $r$-mode oscillation, and also affected by fallback accretion processes. However, anomalous spin variations, particularly sudden enhanced spin-down rates, indicate additional spin-down mechanisms. We propose superradiant spin-down as a potential explanation for these events. By modelling the interplay between conventional and superradiant spin-down channels, we evaluate their impact on neutron star rotational evolution. We also discuss gravitational-wave emission produced by quadrupole deformation, $r$-mode oscillations, and axion-induced bosonic clouds around an isolated neutron star, highlighting their potential as distinct multimessenger probes in upcoming detectors.