On the misalignment of jets in microquasars


★ E-mail: maccaron@sissa.it


We discuss the time-scales for alignment of black hole and accretion disc spins in the context of binary systems. We show that for black holes that are formed with substantial angular momentum, the alignment time-scales are likely to be at least a substantial fraction of the lifetimes of the systems. This result explains the observed misalignment of the disc and the jet in the microquasar GRO J 1655-40 and in SAX J 1819-2525 as probably being caused by the Bardeen–Petterson effect. We discuss the implications of these results on the mass estimate for GRS 1915+105, which has assumed the jet to be perpendicular to the orbital plane of the system and may hence be an underestimate. We show that the time-scales for the spin alignment in Cygnus X-3 are consistent with the likely misalignment of disc and jet in that system, and that this is suggested by the observational data.