Physics of Black Hole-Powered Jets

Supermassive black holes in active galactic nuclei (AGN) can produce highly collimated relativistic outflows of magnetized plasma that extract energy and angular momentum from the black hole - accretion disk system and transport it to interstellar and intergalactic medium. Despite their ubiquity in the Universe, many of the fundamental questions regarding these jets are still open. We do not understand well the launching mechanism of the jets, or their acceleration and collimation. We do not know what turns the jets on and off again. We also do not fully understand the energy dissipation mechanisms that produce the spectacular flares observed in blazars – sources with jets oriented close to our line-of-sight. Answering these questions requires an ability to observationally constrain physical parameters very close to the central engine, where the acceleration and collimation of the flow take place. With its sub-milliarcsecond resolution Very Long Baseline Interferometry (VLBI) technique is the only observational method that allows us to directly image the extragalactic jets near their origin. The research program proposed here takes advantage of the recent leaps in the capabilities of new and existing VLBI arrays in order to address the questions of how the jets are accelerated and collimated by magnetic forces, and where and how is the flow energy dissipated. We will for example use the recently launched Russian space radio telescope RadioAstron in concert with a network of the largest ground-based radio telescopes to obtain the highest ever angular resolution images of AGN jets and directly probe their acceleration and collimation region on spatial scales corresponding only to a few to a few hundred Schwarzschild radii. Furthermore, we will use the newly upgraded Very Long Baseline Array in the US to constrain the magnetic field structure in jets by obtaining high-dynamic-range, multi-frequency, polarization images of transversally resolved jets. The aim of these observations is to provide tests to the current magnetic jet launching and acceleration models. We will also address the question of the location of the main energy dissipation region in AGN jets by analysing our recently assembled, unprecedentedly dense
VLBA and multi-wavelength monitoring data set of quasar 3C279.

Supermassive black holes in active galactic nuclei (AGN) can produce highly collimated outflows of magnetized plasma, commonly termed as jets, which are ejected at speeds close to the speed-of-light from the vicinity of the black hole. This research project aims at better understanding how these jets are formed, how magnetic fields accelerate plasma to such extreme speeds, and what mechanisms cause the spectacular brightness variations in some jets. Our approach takes advantage of recent developments in radio interferometry instrumentation. We will for example use the recently launched Russian space radio telescope RadioAstron in concert with a network of the largest ground-based radio telescopes to obtain the highest ever angular resolution images of these jets and probe their acceleration and collimation region. Moreover, we will use the newly upgraded Very Long Baseline Array to measure the properties of jet magnetic fields through spatially resolved polarization spectra.