Magnetic interactions in orbital dynamics

TL;DR

This paper investigates how magnetic fields of stars influence the orbital dynamics of magnetic or conducting bodies, revealing potential effects like orbital precession, eccentricity pumping, and resonance trapping, especially in close binary systems.

Contribution

It provides a theoretical analysis of magnetic forces on orbiting bodies using the dipole approximation, highlighting conditions for measurable orbital effects in stellar systems.

Findings

Magnetic forces can cause orbital precession in close binaries.

Conducting bodies may experience eccentricity pumping due to stellar magnetic fields.

Magnetic interactions are significant only when the orbit is very close to the star.

Abstract

The magnetic field of a host star can impact the orbit of a stellar partner, planet, or asteroid if the orbiting body is itself magnetic or electrically conducting. Here, we focus on the instantaneous magnetic forces on an orbiting body in the limit where the dipole approximation describes its magnetic properties as well as those of its stellar host. A permanent magnet in orbit about a star will be inexorably drawn toward the stellar host if the magnetic force is comparable to gravity due to the steep radial dependence of the dipole-dipole interaction. While magnetic fields in observed systems are much too weak to drive a merger event, we confirm that they may be high enough in some close compact binaries to cause measurable orbital precession. When the orbiting body is a conductor, the stellar field induces a time-varying magnetic dipole moment that leads to the possibility of eccentricity pumping and resonance trapping. The challenge is that the orbiter must be close to the stellar host, so that magnetic interactions must compete with tidal forces and the effects of intense stellar radiation.