Fleet of Worlds: 200 Years Before the Discovery of the Ringworld (Known Space") <2>

When a chain reaction of supernovae explosions at the core of the galaxy unleashes a deadly wave of radiation that will sterilize the entire galaxy, the Citizens--accompanied by Kirsten Quinn-Kovacs, a descendant of human survivors rescued by the Citizens from a dying starship--flee into the unknown, in a novel set in the Known Space universe. Reprint.