The interaction of gas rich galaxies via mergers or close encounters can give rise to sudden, violent star formation (SF), often accompanied by the presence of an active galactic nucleus AGN. The merger gives rise to a system whose energy is mostly emitted in the IR with a luminosity above 10E11 L_sun. These dusty environments are the scenery of supernova explosions at a high rate as well as of super-massive black hole (SMBH) growth, thus representing excellent laboratories to study the evolution of galaxies. However, such activity in the innermost nuclear regions (<500pc) remains hidden at most wavelengths, including optical, due to the high concentration of dust and gas, and a direct view is only possible using high resolution observations not strongly affected by extinction, such as near-IR and radio. In this talk I will present exciting observations of a “baby” AGN and a tidal disruption event revealed with very long baseline interferometry.