Fleet of Worlds(2007)

Larry NivenEdward M. Lerner

Fleet of Worlds marks Larry Niven's first full novel-length collaboration within his Known Space universe, the playground he created for his bestselling Ringworld series. Teaming up with fellow SF writer Edward M. Lerner, Fleet of Worlds takes a closer look at the Human-Puppeteer (Citizens) relations and the events leading up to Niven's first Ringworld novel.
 
Kirsten Quinn-Kovacs is among the best and brightest of her people. She gratefully serves the gentle race that rescued her ancestors from a dying starship, gave them a world, and nurtures them still. If only the Citizens knew where Kirsten's people came from….

A chain reaction of supernovae at the galaxy's core has unleashed a wave of lethal radiation that will sterilize the galaxy. The Citizens flee, taking their planets, the Fleet of Worlds, with them.

Someone must scout ahead, and Kirsten and her crew eagerly volunteer. Under the guiding eye of Nessus, their Citizen mentor, they explore for any possible dangers in the Fleet's path--and uncover long-hidden truths that will shake the foundations of worlds.