Spline (alien beings)

The Xeelee Sequence is a series of hard science fiction space opera novels, novellas and short stories by British science fiction author Stephen Baxter. The novels span several billion years, describing the future expansion of humanity, its war with its nemesis (an alien Type IV civilization) called the Xeelee, and the Xeelee's own war with dark matter entities called Photino Birds. Other important Xeelee Sequence species include the Qax, the Squeem, and the Silver Ghosts. Several novels also deal with humans and posthumans living in extreme conditions, such as the heart of a neutron star (Flux) or a universe with considerably stronger gravity (Raft).