Radio jets clearing the way through a galaxy: watching feedback in action.

The energy released by an active galactic nucleus (AGN) has a strong impact on the surrounding interstellar medium (ISM). This feedback is considered to be the regulating factor for the growth of the central massive black hole and for the rate of star formation in a galaxy. We have located, using very-long-baseline interferometry, the fast outflow of neutral hydrogen in the young, restarted radio-loud AGN 4C12.50. The outflow is located 100 parsec from the nucleus where the radio jet interacts with the ISM, as well as around the associated radio lobe. These observations show that the radio plasma drives the outflow and removes gas from the central regions and that jet-driven outflows can play a relevant role in feedback mechanisms.