- Paris Observatory
Black holes and galaxies appear to grow in symbiosis. Non-axisymmetric features like bars, and even several embedded density waves in galaxies are necessary to exchange angular momentum and drive the gas to feed the nucleus, Feedback regulates star formation, and can be of radiative or kinetic modes in origin. Gas outflows are energy-driven at the beginning and may become momentum driven, with lower efficiency. If the regulation appears to work quite well in galaxy clusters to regulate cooling flows, it is still debated in individual galaxies.