What characteristics must a binary star have to be a good candidate for a black hole? What characteristics must a binary star have to be a good candidate for a black hole? One member of the binary system must be invisible, since no radiation can leave a black hole. One member of the binary system must be an A-spectral type star since those are the ones that form black holes. One member of the binary system must have very high mass yet be small in size. The pair must radiate energetic X-rays, since such X-rays arise from accretion disks in which matter is being pulled into a black hole. Must detect nova explosions on a regular basis, as they are associated with black holes