Consequences of a possible jet-star interaction in the inner central parsec of Centaurus A

Abstract

The jet-counterjet system of the closest radio-loud active galaxy Centaurus A (Cen A) can be studied with Very Long Baseline Interferometry (VLBI) on unprecedented small linear scales of ∼ 0.018 pc. These high-resolution observations provide essential information on jet emission and propagation within the inner parsec of an AGN jet. We present the results of a kinematic study performed within the framework of the Southern-hemisphere AGN monitoring program TANAMI. Over 3.5 years, the evolution of the central-parsec jet structure of Cen A was monitored with VLBI. These observations reveal complex jet dynamics which are well explained by a spine-sheath structure supported by the downstream acceleration occurring where the jet becomes optically thin. Both moving and stationary jet features are tracked. A persistent local minimum in surface brightness suggests the presence of an obstacle interrupting the jet flow, which can be explained by the interaction of the jet with a star at a distance of ∼ 0.4 pc from the central black hole. We briefly discuss possible implications of such an interaction regarding the expected neutrino and high-energy emission and the effect on a putative planet