RASPO · non-thermal Radiation from AStrophysical jets: from theory of Plasma turbulence to Observations

non-thermal Radiation from AStrophysical jets: from theory of Plasma turbulence to Observations

The centers of galaxies host supermassive black holes that can reach a million or even a billion solar masses. Supermassive black holes can eject narrow beams of material that travel close to the speed of light. These jets shine through the entire spectrum of the electromagnetic radiation, and are observed from low frequency radio waves to very high energy gamma-rays. Even if jets have now been studied for more than a century, we do not fully understand how they are launched, and we do not fully understand how the observed radiation is produced. An interesting possibility (originally proposed by Blandford and Znajek) is that magnetic field lines are anchored to the supermassive black hole. Since the black hole rotates, electrons and ions are accelerated as they move away from the black hole along the field lines. The accelerated electrons can emit the observed radiation via two channels: by gyrating about the magnetic field lines (synchrotron radiation), and by scattering to higher energies the ambient photons produced near the black hole or by the jet itself (inverse Compton radiation). The aforementioned theoretical paradigm leads to a testable prediction: jets should be magnetically dominated, i.e. most of their energy should be stored in their electromagnetic fields. Equivalently, the kinetic energy of the particles within the jet should be much smaller than the electromagnetic energy. The main goal of this project is testing whether this paradigm for the launching of jets by rotating magnetized black holes is consistent with observational constraints. The most important observational constraints are the following. Theoretical models of jets should be able to reproduce the observed spectral energy distribution, i.e. the radiation power emitted by the jet per unit photon wavelength. Theoretical models should also reproduce the polarization degree of the observed radiation (i.e. the fraction of radiation that is polarized) and the polarization angle (i.e. the direction of the electric field of the wave). Radio, optical and X-ray polarization measurements are currently available. In this project, we develop new models of the jet emission where the emission zone (where the observed radiation is produced) is magnetically dominated. We test these models against spectral and polarimetric observations of jets launched by supermassive black holes. We focus on blazars, a particular class of jets that point nearly along our line of sight. Focusing on blazars has the main advantage that the radiation from the jet is strongly beamed due to Doppler effect. Then, blazars can be observed more easily than misaligned jets.

Data: CORDIS, © European Union