Title: The Kelvin-Helmholtz instability at the boundary of relativistic magnetized jets

Abstract: We study the linear stability of a planar interface separating two fluids in relative motion, focusing on conditions appropriate for the boundaries of relativistic jets. The jet is magnetically dominated, whereas the ambient wind is gas-pressure dominated. We derive the most general form of the dispersion relation and provide an analytical approximation of its solution for an ambient sound speed much smaller than the jet Alfven speed, as appropriate for realistic systems. The stability properties are chiefly determined by the angle  between the wavevector and the jet magnetic field. For wavevector perpendicular to the magnetic field, magnetic tension plays no role, and our solution resembles the one of a gas-pressure dominated jet. Here, only sub-Alfvenic jets are unstable. For wavevector parallel to the magnetic field, the free energy in the velocity shear needs to overcome the magnetic tension, and only super-Alfvenic jets are unstable. Our results have important implications for the propagation and emission of relativistic magnetized jets.

Title: Stellar Formation and Evolution in the AGN Disk

Abstract: Study of stellar objects embedded in AGN accretion disks around massive Black Holes have been motivated by i) the disk of stars that formed in-situ in the galactic center; ii) the redshift independence of metallicity in AGN disks, which also suggest in-situ pollution; iii) massive LIGO-Virgo gravitational wave sources that possibly evolved in a gas rich environment, and iv) quasi-periodic eruptions connected to star-disk collisions. 
In this talk, I will introduce some recent progress on star formation in AGN disks, as well as the accretion, structure and lifetime of embedded massive stars and their co-evolution with AGN disks. In relation to the AGN channel for LIGO-Virgo events, I will discuss how tidal interaction in hierarchical systems influences the accretion, migration and mutual interaction of disk-embedded objects, and therefore their merger properties. I will emphasize that with the environment of AGN disks (featuring strong turbulence, radiation pressure prevalence, dynamical crowded population of stellar mass objects) being much more extreme than protoplanetary disks, established theories from planet formation should be transplanted into the AGN context with caution.