Evidence for initial jet formation by an accretion disk in the radio galaxy M87

The nearby E0 galaxy M87 in the Virgo Cluster contains one of the nearest examples of a powerful non-thermal jet source. In addition, HST spectroscopy of its nucleus give strong evidence for the presence of a ≈3×10⁹ M_⊙ central black hole (corresponding to Schwarzschild radius R_s～0.0004 pc). These two facts together make M87 the best possible target for studying the initial jet formation and collimation process. Herein we report new 43 GHz VLBI observations of the nucleus of this galaxy, which clearly show the jet opening angle expanding rapidly as one approaches the core on scales ～0.01 pc. We believe we have, for the first time, imaged the initial collimation region of a powerful extragalactic jet. We find significant collimation occurring on scales of 30–100 R_s, and argue this is consistent with expectations for poloidal collimation by a rotating accretion disk.