Gravitational Wave Emission by Accretion of Matter and Magnetic Deformation in Fast Rotating White Dwarfs

TL;DR

This paper investigates gravitational wave emission mechanisms in fast-spinning white dwarfs due to accretion and magnetic deformation, estimating detectability with space-based GW detectors for specific systems and conditions.

Contribution

It provides new estimates of GW amplitudes and luminosities for fast-spinning white dwarfs considering two emission mechanisms, and assesses their detectability by future space detectors.

Findings

AE Aquarii and RX J0648.0-4418 detectable if accreted mass ≥ 10^{-5} M_sun

Systems require magnetic fields > 10^9 G for GW detection by BBO

Some SGRs/AXPs as WD pulsars detectable by BBO and DECIGO

Abstract

We discuss some aspects of Sousa et al.(2020a, 2020b) concerning two mechanisms of gravitational wave (GW) emission in fast-spinning white dwarfs (WDs): accretion of matter and magnetic deformation. In both cases, the GW emission is generated by an asymmetry around the rotation axis of the star. However, in the first case, the asymmetry is due to the amount of accreted matter in the magnetic poles, while in the second case it is due to the intense magnetic field. We have estimated the GW amplitude and luminosity for three binary systems that have a fast-spinning magnetized WD, namely, AE Aquarii, AR Scorpii and RX J0648.0-4418. In addition, we applied the magnetic deformation mechanism for SGRs/AXPs described as WD pulsars. We found that, for the first mechanism, the systems AE Aquarii and RX J0648.0-4418 can be observed by the space detectors BBO and DECIGO if they have an amount of accreted mass of $\delta m \geq 10^{-5}M_{\odot }$. For the second mechanism, the three systems studied require that the WD has a magnetic field above $\sim 10^{9}$ G to emit GWs that can be detected by BBO. Furthermore, we found that some SGRs/AXPs as WD pulsars can be detected by BBO and DECIGO, whereas SGRs/AXPs as highly magnetized neutron stars are far below the sensitivity curves of these detectors.