as "The Xeelee Flower" the following year). He incorporated powerful off-stage aliens to explain the story's titular artifact, and in pondering the backstory began to flesh out the basics of what would later become the main players and setting of the Sequence: a universe full of intelligent species that live in the shadow of the incomprehensible and god-like Xeelee. Plot overview The overarching plot of the Xeelee Sequence involves an intergalactic war between humanity and the Xeelee, and a cosmic war between the Xeelee and the Photino Birds, with the latter two being alien species that originated in the early universe. The technologically advanced Xeelee primarily inhabit supermassive black holes, manipulating their event horizons to create preferable living environments, construction materials, tools, and computing devices. The Photino Birds are a dark matter-based species that live in the gravity wells of stars, who are likely not aware of baryonic life forms due to dark matter's weak interactions with normal matter. Due to the inevitable risk of their habitats being destroyed by supernovae and other consequences of stellar evolution, the Photino Birds work to halt nuclear fusion in the cores of stars, prematurely aging them into stable white dwarfs. The resulting dwarfs provide them with suitable habitats for billions of times longer than other types of stars could, but at the expense of other forms of life on nearby planets. The Photino Birds' activities also effectively stop the formation of new black holes due to a lack of Type II supernovae, threatening the existence of the Xeelee and their cosmic projects. After overcoming a series of brutal occupations by extraterrestrial civilizations, humanity expands into the galaxy with an extremely xenophobic and militaristic outlook, with aims to exterminate other species they encounter. Humans eventually become the second-most advanced and widespread civilization in the Milky Way galaxy, after the Xeelee. Unaware of the Photino–Xeelee war and the existential ramifications of what is at stake, humanity come to the (unwarranted) conclusion that the Xeelee are a sinister and destructive threat to their hegemony and security. Through a bitter war of attrition, humans end up containing the Xeelee to the galactic core. Both humans and the Xeelee gain strategic intelligence by using time travel as a war tactic, through the use of closed timelike curves, resulting in a stalemate for thousands of years. Eventually, humanity develops defensive, movable pocket universes to compartmentalize and process information, and