Yes, supermassive black holes can have objects other than stars orbiting around them. While stars are the most common objects found in the vicinity of supermassive black holes, there are other possibilities, including smaller black holes.
Smaller black holes, known as stellar-mass black holes, can form in regions where stars are densely packed, such as in the centers of galaxies. These stellar-mass black holes can interact gravitationally with a supermassive black hole and become part of its immediate environment. They can either be captured by the gravitational pull of the supermassive black hole or form binary systems, where a smaller black hole orbits around the larger one.
These binary systems of black holes, known as black hole binaries, can have interesting dynamics. Over time, through processes such as gravitational interactions and mergers, the black holes can spiral in closer to each other and eventually merge, emitting gravitational waves in the process. The detection of gravitational waves by observatories like LIGO and Virgo has provided evidence for the existence of such binary black hole systems.
It's worth noting that the direct observation of smaller black holes orbiting supermassive black holes is challenging due to their small size and the limited resolution of current observational techniques. However, through indirect methods and gravitational wave detections, scientists have inferred the presence of these smaller black holes in the vicinity of supermassive black holes.