Near-infrared (I band) light curves for QZ Vulpeculae, adapted from Chevalier and Ilovaisky (1993).[1] The data were collected over a 10 night period in July 1991. Data collected on different nights are plotted with different colors. The shape of the light curve changed over a period of approximately two days, leading to different shapes on even or odd numbered days.
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.[6]