| Relativistic ejections are a common consequence of accretion processes onto black holes and neutron stars. They are associated with supermassive black holes as large as million-billion solar masses in active galactic nuclei (AGN) as well as stellar mass black holes and neutron stars in X-ray binaries (XRBs). Assuming that the physical timescales related to the accretion and ejection processes scale with the mass of the compact object, 1 day in an XRB corresponds to ~300000 years in an AGN. For this reason XRBs represent a unique tool to investigate the jet emission mechanisms in relation to the accretion conditions, on timescales shorter than human life-time.
I will present my studies of an XRB characterized by a faint jet, representative of a growing family of sources. I will show that faint jet emitters can significantly help to understand the coupling between the inflow and the outflow processes. Jets from compact objects are also a source of energetic particles that can inflate cavities and nebulae that deeply change the surrounding medium. This kinetic feedback from AGN acted to regulate the growth of galaxies, helping to determine the current form of the universe. Recently it has been discovered that XRBs act on the interstellar medium in a way similar to AGN. I will discuss some recent results, showing how LOFAR will improve our knowledge of these phenomena.
Image caption: In studies of accreting black holes in binary systems, empirical relations have been proposed to quantify the coupling between accretion processes and ejection mechanisms. These processes are probed, respectively, by means of X-ray and radio observations. Although these correlations were thought to be universal, many sources have been found to produce jets that are fainter than expected from the earlier correlations. This figure shows a recent collection of simultaneous X-ray and radio data for a number of black hole binaries in the hard state. The study of the sources characterized by a faint jet is fundamental to understand the accretion/ejection coupling.