# Why do X-ray binaries such as GRS-1915 have active and quiet states?

X-ray binaries such as GRS-1915 feature a black hole and a regular star. The x-ray luminosity is likely related to the rate of mass flow into the black hole from the star so when there is a lot of mass flow the x-ray luminosity is high but this explanation seems to just beg the question as to why the mass flow would change over time.

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