Driving massive galaxy outflows with supermassive blackholes
Active galactic nuclei (AGN) are supermassive black holes at the centers of galaxies that are accreting material onto their hot circumnuclear disks, releasing the energy in bursts of radiation or as particle jets moving at close to the speed of light. These energetic outbursts in turn drive outflows of ionized, neutral, and molecular gas that can extend over thousands of light-years and move at speeds of hundreds of kilometers per second. The gas flows can be launched directly from the hot accretion disc, though radiation pressure on the dust that is mixed in with the gas, by hot thermal winds, or other mechanisms that generate hot bubbles of gas. By driving the gas out of the galaxy, an active nucleus restricts the fuel available for further star formation and slows down the galaxy’s growth. The mechanism is also self-limiting, since it ultimately suppresses gas accreting onto the black hole. Astronomers tracking the rate of star formation across cosmic time believe this process, called quenching, is responsible for the dramatic decline in star formation since the peak of star-formation activity about ten billion years ago.
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