Epsilon Ionis is a binary star system, located about 30 light years from the Kyr system, consisting of a star with a black hole in a highly elliptical orbit. The primary star had just gone nova not too long before a point in the 2260s when the USS Enterprise was nearby at Kyros, causing an intense wave of radiation to close in on that position. The radiation was picked up by the black hole, from the nova star, as energy in a gravitational field. Because of the fast motion of the black hole as it approached the perihelion in its ellipse motion, a slingshot effect occurred, propelling parts of a radiation field at warp 10 in the direction of Enterprise. (TOS novel: Spock, Messiah!)