SILVER GHOSTS

The Silver Ghosts are an highly advanced non-humanoid species. They are most unique in appearance, being large floating spheres of silvery chrome protecting a fragile inner body. They are largely benevolent explorers, concerned more with science and experimentation than conquest. They come from a world devastated by a supernova early in their history; despite being abandoned to the cold of space ("the Heat Sink" as they called it), the Ghosts survived. The Ghosts are often associated with forbidden experiments, as they frequently toy with the laws of nature to advance their own knowledge.
Source: Stephen Baxter, Xeelee Sequence