Intermittent activity of radio sources. Accretion instabilities and jet precession.

We consider the radiation pressure instability operating on short timescales (10³ - 10⁶ years) in the accretion disk around a supermassive black hole as the origin of the intermittent activity of radio sources. We test whether this instability can be responsible for short ages (<10⁴ years) of Compact Steep Spectrum sources measured by hot spots propagation velocities in VLBI observations and statistical overabundance of Gigahertz Peaked Spectrum sources. The implied timescales are consistent with the observed ages of the sources. We aslo discuss possible implications of the intermittent activity on the complex morphology of radio sources, such as the quasar 1045+352, dominated by a knotty jet showing several bends. It is possible that we are whitnessing an ongoing jet precession in this source due to internal instabilities within the jet flow.