GS 2000+25

GS 2000+25 is an X-ray binary system in the constellation Vulpecula, consisting of a late K-type star and a black hole. It is also an X-ray nova.
Fumiyoshi Makino and the Ginga satellite team discovered GS 2000+25, in April of 1988. A few days later a star, variable in visible light, was identified at its position. It received its variable star designation, QZ Vulpeculae, in 1989.

Properties

Because the black hole is more massive than the companion star, it is the primary of the system. The black hole has a mass of about 5 solar masses while the companion has a mass of about 0.5 solar masses. Because the companion star has a low mass, the system is a low-mass X-ray binary.