gravitomagnetic field

A gravitomagnetic field is a field analogous to a magnetic field but is an aspect of gravitation rather than of electromagnetism. It does not involve magnetism, rather its relationship to gravity is analogous to magnetism's relation to the Coulomb force: magnetism can be explained as a relativistic effect on the Coulomb force, specifically because changes in the electric field take time to affect something at a distance (because the speed of light in a vacuum is the speed of any possible effect), and gravity is affected analogously. This gravitational effect is generally insignificant other than within some regimes of strong-field gravity under rotation. The terms gravitomagnetism and gravitoelectromagnetism (GEM) are used for such effects, and a set of equations analogous to the Maxwell's equations serves as an effective field theory for the regime. The effects have been hypothesized to be part of the mechanism generating relativistic jets. An exotic possibility under current consideration is whether galaxy rotation curves might be explained by gravitomagnetic effects, i.e., whether gravitomagnetism could explain the observed phenomena that motivates the dark matter concept.

Note that I've also seen the term gravito-magnetism and similar phrases used for phenomena that involve both gravity and magnetism, e.g., of charged particles and plasma, so be aware.