The IAA-CSIC offers a 4 year PhD contract in the framework of the Project “Severo Ochoa”. Candidates are expected to carry out their activity in research line: Galaxy Evolution, Cosmology and Black Holes Accretion. Supervisor: Iván Agudo (firstname.lastname@example.org) Active galactic nuclei (AGN) are the most energetic objects known so far, and are produced by the fall of gas at the center of some galaxies towards their central supermassive black hole (SMBH). Among the large diversity of known AGN, there is a fundamental difference between radio-emitting AGN and non-radio-emitting AGN, the first being those that produce powerful relativistic jets of magnetized and highly energized plasma. These jets in AGN are propelled along the rotation poles of the accretion disk-SMBH system. One of the most exotic types of radio loud AGN is blazars, a class defined by the extreme variability of its non-thermal radiation from radio wavelengths to the highest gamma-ray energies. The remarkable properties of blazars include apparent superluminal motions up to ~ 50 times the speed of light, extreme changes in total flux and linear polarization on time scales of up to minutes, and extremely variable gamma-ray luminosities that may exceed those of other bands of the electromagnetic spectrum in up to 3 orders of magnitude. In blazars, the relativistic jets emit most of their radiation (and point) at an angle of <10º with regard to the line of sight, which makes them to shorten their time scales of variability to give blazars the remarkable properties by which they are known. Other types of radio-loud AGN include radio galaxies, with jet viewing angles >> 10º, that display much longer time scales of variability, and much less luminous emission at all ranges of the spectrum. At these radio wavelengths, relativistic jets in radio galaxies are visible in their entirety from the innermost scales near the central SMBH, to distances that even frequently exceed the size of the host galaxy. This PhD project is guided by the motivation to answer some of the main current questions in the field of AGN research, i.e.: a) What are the properties of the environment near the central supermassive black hole (accretion flow)? Why do some AGN produce jets and others not? b) What particle acceleration mechanisms capable of keeping jets in AGN collimated until such long distances are predominant? What is the composition (e--e+ or e--p+) of those jets? c) What is the region of production of gamma-ray flares? What is their dominant very-high-energy emission mechanism? To attach these questions, a combination of astronomical observations and numerical simulations will be carried out for the interpretation of the multi-wavelength emission (at all available spectral range from very high energy gamma rays to radio), and linear and circularly polarized millimeter emission in a set of different AGN and in Sgr A * (the supermassive black hole at the center of the Milky Way). With this, the student will infer the structure of the magnetic fields in the plasmas responsible for the emission, the composition of the plasmas, the emission models in all the ranges of the spectrum, and the density and magnetic field of the surrounding interstellar material. The main tasks to develop during the PhD research will include: 1.- Exploitation of the POLAMI and MAPCAT databases accumulated by the group in the millimeter and optical spectral ranges, respectively. 2.- Planning, development, and analysis of complementary astronomical observations in facilities accessible by the group at all available spectral ranges from the very-high-energy gamma-rays (including Fermi, MAGIC, and even CTA in the near future), to radio wavelengths (including very long baseline interferometers such as the EVN or the VLBA), passing through microwaves (e.g. NOEMA and IRAM 30m Telescope), and the optical (e.g. Calar Alto Observatory, Roque de los Muchachos Observatory). 3.- Development of Python based software for data analysis. 4.- Development of numerical tools for the simulation of non-thermal emission around SMBH systems, including jets. 4.- Physical interpretation of the observational and numerical data. Good skills in relativity, plasma physics, and radiation physics would be an advantage.