Active Galactic Nuclei (AGN) are among the most energetic surces of radiation in the universe. They emit billions of solar luminosities from their cores which are only few parsecs in size. The ‘central engine” of AGN is powered by accretion onto massive black holes. As far as we know today, all galaxies host “supermassive’ – meaning milions to billions of solar masses – black holes in their nuclei. When these black holes accrete matter from their vicinity, a fraction of the enormous gravitational energy is released as electromagnetic radiation. Some AGN show huge outflows (“jets”, “lobes”) spanning up to several megaparsecs. Nowadays, there is a general understanding of AGN activity, which is summarized in the “viewing angle unification scheme”. However, many details are still unknown.

My research is focused on questions like

– What is the intrinsic structure and geometry of AGN outflows?

– What are the fundamental properties of the central black holes?

– How variable is the AGN activity?

Established in the 1930s, radio astronomy is a relatively recent branch of observational astronomy. It differs from observations at all other energies on a very fundamental level: only in radio astronomy, electromagnetic radiation is recorded as waves with known amplitudes and phases. All other wavelength regimes rely on the detection of photons which “only provide information on intensities. Covering wavelengths from meters to millimeters, principal targets of radio observations are non-thermal radiation – especially from AGN -, molecular lines, and cold interstellar matter.

An especially fascinating technology using radio telescopes is interferometry. By correlating the signals of several radio antennas, one obtains a “telescope” with an effective resolution only limited by the maximum size of the telescope array. The largest arrays – VLBI – span across the entire earth and achieve angular resolutions as small as 50 microseconds of arc. My current research makes use of some of the largest radio interferometers existing like PdBI, VLBI, and, most recently, the Korean VLBI Network.

[Homepage] https://astro.snu.ac.kr/~trippe/