  In this paper we push forward and exploit an analogy between the morphologies
of the X-ray cavities observed in some galaxy clusters, and the optically
deficient point-symmetric bubbles occurring in some planetary nebulae (PNe).
Point-symmetric PNe are thought to be shaped by stellar binary interactions;
namely, the presence of a companion to the PN's progenitor star is required. We
suggest that similar point-symmetric structures in the X-ray cavities of galaxy
clusters might be associated with the presence of massive binary black holes. A
systematic cataloguing of high-resolution images of the diffuse X-ray emission
at the core of galaxy clusters might contribute to individuate massive binary
black holes.
