We present the results of a VLBI Space Observatory Programme ( VSOP ) observation of the subparsec structure in Centaurus A at 4.9 GHz .
The observation produced an image of the sub-parsec jet components with a resolution more than 3 times better than images from previous VLBI monitoring campaigns at 8.4 GHz and more than 2 times better than the previous 22 GHz studies .
Owing to its proximity , our Centaurus A space-VLBI image is one of the highest spatial resolution images of an AGN ever made — 0.01 pc per beam — comparable only to recent 43 GHz VLBI images of M87 .
The elongated core region is resolved into several components over 10 milli-arcseconds long ( 0.2 pc ) including a compact component of brightness temperature 2.2 \times 10 ^ { 10 } K. The counter jet was detected : if we assume jet–counterjet symmetry , a relatively slow jet speed , and a large viewing angle , as derived from previous observations , the image allows us to investigate the distribution of ionized gas around the core , which is opaque at this frequency due to free-free absorption .
We also analyze the jet geometry in terms of collimation .
Assuming the strongest component to be the core , the jet opening angle at \sim 5000 r _ { s } from the core is estimated to be \sim 12 ^ { \circ } , with collimation of the jet to \sim 3 ^ { \circ } continuing out to \sim 20 , 000 r _ { s } .
This result is consistent with previous studies of the jet in M87 , which favor MHD disk outflow models .
Future space VLBI observations at higher frequencies will probably be able to image the collimation region , within 1000 r _ { s } of the center of Centaurus A , together with the accretion disk itself .