Impact of dipolar magnetic fields on gravitational wave strain by galactic binaries

TL;DR

This paper studies how magnetic dipole interactions in galactic binaries affect gravitational wave signals, revealing a secular drift and frequency shifts that could influence LISA's measurements.

Contribution

It derives and analyzes the impact of magnetic dipole-dipole interactions on gravitational wave signals from galactic binaries, a novel consideration for GW data interpretation.

Findings

Magnetic interactions cause a secular drift in orbital mean longitude.

The drift magnitude depends on magnetic moments and orbital semi-major axis.

Magnetic effects shift the main gravitational wave frequency observed by LISA.

Abstract

White dwarfs (WDs) and neutron stars (NSs) are among the most magnetized astrophysical objects in the universe, with magnetic fields that can reach up to $10^9\,\mathrm{G}$ for WDs and up to $10^{15}\,\mathrm{G}$ for NSs. The galaxy is expected to be populated with approximately one hundred million of double WD and millions of NS-WD binaries. Throughout the duration of the mission, the Laser Interferometer Space Antenna (LISA) will observe gravitational waves (GWs) emitted simultaneously by more than ten thousand of such galactic binaries. In this paper, we investigate the effect of the magnetic dipole-dipole interaction on the GW signal emitted by magnetic galactic binaries. We derive the secular equations governing the orbital and rotational motion of these objects. Then, we integrate these equations both numerically and analytically. We conclude that the overall visible effect is an additional secular drift of the mean longitude. This drift is proportional to the product of the magnetic moments and is inversely proportional to the $7/2$ power of the semi-major axis. Finally, we show that, at zeroth-order in eccentricity, the magnetic dipole-dipole interaction shifts the main frequency of the gravitational strain measured by LISA.