Continuous gravitational waves from magnetized white dwarfs: Quantifying the detection plausibility by LISA

TL;DR

This paper assesses the potential for detecting continuous gravitational waves from highly magnetized white dwarfs using future space-based detectors like LISA, highlighting the importance of magnetic deformation and observational timescales.

Contribution

It models magnetic deformation effects on white dwarfs and evaluates their detectability by upcoming gravitational wave observatories, providing new insights into WD magnetic fields and gravitational wave signals.

Findings

LISA could detect dozens of highly magnetized white dwarfs in the galaxy.

A specific white dwarf, ZTF J1901+1458, is detectable with four years of data.

Detection timescales are constrained by magnetic field strength and age of the white dwarf.

Abstract

White dwarfs (WDs) are frequently observed to have strong magnetic fields up to $10^9$ G and expected to have a possible internal field as high as $\sim 10^{14}$ G. High internal fields can significantly deform a WD's equilibrium structure, generating a quadrupole moment. If the rotation axis is misaligned with the magnetic axis, the deformation can lead to the emission of continuous gravitational waves (CGWs). We examine the potential for detecting CGWs from magnetized WDs with future space-based detectors such as LISA, ALIA, DECIGO, Deci-Hz, BBO and TianQin. We model the field-induced deformation and compute the resulting GW strain, incorporating amplitude decay due to angular momentum loss from electromagnetic and gravitational radiation. This sets a timescale for detection -`active timescale' of $10^{5-6}$ yr, requiring observation while the object remains sufficiently young. Our results suggest that LISA could detect a few dozens of highly magnetized WDs across the Galaxy during its mission. As a specific case, we investigate ZTF J1901+1458- a compact, massive, fast-rotating, and strongly magnetized WD with spin period $\sim416$ s and inferred surface field $\sim10^{9}$ G. We find that this object would be detectable by LISA with four years of continuous data. This highlights the potential of CGW observations to probe magnetic field structure in WDs and their role in type Ia supernova progenitors.