The gravitational field of a spinning pencil of light

An exact solution of Einstein's equations in a vacuum (outside of singularities), belonging to Kundt's class and Petrov type N, is interpreted as the metric of a spinning pencil of light (a linear source infinitely extended in one direction and moving with the speed of light). It is shown that the gravitational fields of two parallel pencils of light do not interact with each other, i.e., the superposition of the metrics of two parallel pencils of light is an exact solution of Einstein's equations in a vacuum. © 1989 American Institute of Physics.