"The supermassive black hole is sucking interstellar gas, but at the same time it is affecting the star-formation history of the galaxy with its powerful winds," Tombesi said. "Astrophysicists describe this process as a feedback between the central supermassive black hole and the galaxy, which on very long timescales regulates their co-evolution." http://news.yahoo.com/black-hole-winds-quench-star-formation-entire-galaxies-183105298.html I received a warning from someone here about two years ago after asking if control systems theory, feedback, and equilibrium could be at play in situations like the above. So I felt stupid and shut up. Today I learnt it is actually thought about in this way. Thanks.