Accretion-related feedback: star formation, black hole accretion, explosive transients

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Many of the most important problems in astrophysics arise because of energetic feedback – the coupling of energy from a compact engine (like a star, neutron star, or black hole) into its own fuel supply (a stellar envelope, or a collapsing molecular cloud, or a spiral galaxy). The projects within this proposal are designed to sort out feedback interactions in several key contexts. ******First, most of the stars created within spiral galaxies like ours are the product of clustered star formation, in which hundreds to thousands of stars are born together in a tumultuous, turbulent collapse. Here, starlight heats and pressurizes the gas, altering the masses of later stellar generations; at the same time, winds, jets, and light (and ultimately supernovae) work to clear the mass reservoir, allowing the cluster to disperse. However, current estimates set these effects too weak to clear matter effectively; but there is evidence it must be. Two of the proposed projects will improve upon these estimates with more sophisticated studies of radiation transfer and stellar wind evolution within the cluster-forming zone; a third analyzes observations of a giant cluster-forming site in the Milky Way. ******Second, the field of gravity wave astronomy is only a year old, but detections will soon shed much light on the origins of stellar-mass black hole binaries. Almost certainly the outcome of stellar collapse, a fraction of these are born in the brilliant gamma-ray bursts thought to involve a collapsing, rapidly rotating massive star. Moreover, one hole may plunge through the envelope of its companion star (in a leading proposed scenario). In either case, an accretion disk forms around the black hole and, since photons are trapped, a mass-loaded wind will emanate from the disk. Energetic feedback from these winds has a strong effect on the star that feeds the disk, dramatically altering the outcome in ways I intend to predict and simulate. ******Third, modern astronomical surveys are capable of tracking time-variable events like supernovae, gamma-ray bursts, and related phenomena like stellar outbursts and tidal disruption events, many of which result from the reaction of a star's envelope to energy output from its core. I and my students will work to quantify poorly-understood classes of explosions, including non-spherical supernovae and shock-driven outbursts that do not destroy the star, while also analyzing the data of a current survey and preparing for much larger ones.