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GRS 1915+105 is an X-ray binary containing an accreting stellar-mass black hole. Gas supplied by its companion forms an accretion disk; changes in that gas produce strong, variable X-ray emission. Its radio-emitting jets make it an example of a microquasar.

The thermal disk spectrum has been used to estimate the black-hole spin by fitting a relativistic disk model. The inference depends on quantities including mass, distance, inclination and the disk's physical state. It therefore illustrates how a bright spectrum constrains a compact object through a model, rather than providing a direct measurement of the event horizon.^[ref]

A microquasar is an accreting stellar binary whose compact object launches relativistic jets, providing a small-scale analogue of a jet-producing active galactic nucleus. The name refers to the analogy between accretion and outflow, not to a miniature galaxy. The accretor may be a black hole or a neutron star.

A revealing observation is a sequence of high-resolution radio images, showing emitting knots moving away from the compact central source. In GRS 1915+105, such observations demonstrated strikingly rapid apparent motions. If a knot moves at speed $\beta c$ at angle $\theta$ toward the observer, light-travel delays giveFor the illustrative values $\beta =0.9$ and $\theta =30^{\circ }$, this is approximately $2.04$: apparent superluminal motion despite a locally subluminal speed. The receding jet has a different arrival-time factor. Comparing both sides and the source distance therefore constrains geometry, rather than measuring a speed directly from one image.^[ref]