2008ApJ...677L..47D

The presence of intergalactic star-forming regions within galaxy clusters shows that stars may form well away from a host galaxy. On larger scales, the existence of distorted isolated galaxies hosting star formation, apparently triggered by unseen companions, challenges our understanding of galaxy interactions and evolution. Moreover, most galaxies contain one or more massive central black holes that can be ejected by gravitational-radiation-induced recoil or by gravitational slingshot. In this Letter we examine the effect of a runaway supermassive black hole (RSMBH) passage through the intergalactic medium using the impulse approximation. Even if ejected at high speed, our analytical estimate indicates that SMBHs are able to ignite star formation efficiently in the wake of their trajectories. Cluster-bound RSMBHs may control intergalactic star formation and have substantial influence on the evolution of low-mass galaxies. Star formation induced by RSMBHs or, as we dub it, the invisible-hand mechanism may have had a very relevant role during the quasar epoch when most SMBHs formed.