Galaxy Evolution

The way an active central black hole regulates its galaxy — its winds and jets heating and expelling gas, quenching star formation, and explaining the tight link between a galaxy's black-hole mass and its bulge.

How galaxies grow and change over cosmic time — assembling from smaller pieces, forming stars, exhausting or losing their gas, and transforming from blue, star-forming disks into red, quiescent ellipticals.

The gravitational give-and-take of galaxies passing close without fully merging — drawing out tidal tails and bridges, triggering star formation, and, in a direct hit, punching out a ring galaxy.

The collision and coalescence of two galaxies. Mergers trigger bursts of star formation, funnel gas to the central black hole, and can turn two spirals into a single elliptical — a driving force of galaxy evolution.

The shutdown of star formation in a galaxy, as it loses or is stripped of its cold gas, or has it heated by feedback — leaving a red, passively-evolving elliptical or lenticular of ageing stars.

A phase of exceptionally intense star formation, forming stars far faster than a galaxy can sustain — often triggered by a merger or interaction and driving powerful galactic winds. M82 is the archetype.