Forerunner fleet weaponry 2

A planetary system is mostly empty, even the greatest of worlds being lost in the immensity of billions of kilometers of space. Like their former human allies, the San’Shyuum had evolved on a water-rich world not far from a yellow star, within a temperate zone that allowed only a narrow range of weather. Now, however, ten thousand years after their defeat, the system was surrounded by trillions of vigilants that constantly wove in and out of space-time, sometimes so rapidly that they seemed to shape a solid sphere. This sphere extended to a distance of four hundred million kilometers from the star, and thus did not encompass four impressive gas giants whose orbits lay beyond that limit.
(Halo:Cryptum; Ch.14)