Active Black Holes: the shadow & the jets
Black Holes can not be observed directly - but their quasi-silhouette (or shadow) can, as the observations of M87 by the Event Horizon Telescope observations show (more here).
The powerful jets that are emitted in both directions along the spin axis of the Black Hole have been observed and studied since many decades. Jets used to be a radio-phenomenon only. We now know, that jets are a multi-wavelength pheonomenon and emit radiation up to the high energies.
The best method to study jets in the vicinity of active Black Holes is Very Long Baseline Interferometry (VLBI). By making use of radio telescopes distributed on different continents, a virtual gigantic telescope with earth-diameter can be generated. This guarantees the highest possible resolution - and the best view on the inner regions around active Black Holes or even binary black holes. Some results of our research are sketched below.
TXS 0506+056 - IceCube neutrino seems to have been generated in a cosmic collider
OJ 287 - deciphering the Rosetta stone of blazars (more to come)
3C454.3 - Detection of an arc-like structure around the core
3C454.3 is an Active Galactic Nucleus (AGN) - a Quasar. This active Black Hole radiates extremely luminous (one of the brightest gamma-ray emitting AGN in the sky). Several enigmatic properties of the radio jet had been discovered and reported. We just found an arc-like feature around the parsec-scale core region. This arc seems to expand with apparent superluminal velocity. This is most likely the first such structure that has been observed and the physical origin is not clear yet. More here.
0735+178 - Switching between apparent stationarity and apparent superluminal motion
Two images of the same Active Galactic Nucleus (a BL Lac Object) at different times.
And the corresponding kinematic behaviour of the jet components.
Thus - apparent superluminal motion seems to be a state/phase of an Active Galactic
Nucleus and can change (Britzen et al., 2010, A&A, 515, 105).
1803+784 - a jet curls into shape and back
The evolution of the jet ridge line starts (1994.67) with the straight (solid dark) line - and evolves into a sinusoidal shape (2000.46). Jet components do not move outwards (away from the Black Hole) but remain at similar core distances. Instead they move perpendicular to the jet direction - up and down (Britzen et al., 2010, A&A, 511, 57).
