Nathan Smith
The interaction between a supernova blast wave and dense circumstellar material (CSM) provides a unique way to investigate the very latest-phases in the pre-core collapse evolution of massive stars, because mass shed by the star in the preceeding decade is illuminated and shock heated. Recent studies of such supernovae have shown that these late phases of stellar evolution must, in some cases, be punctuated by violent instabilities that precede the supernova by a few years to decades. The cause of these and the types of stars which fall subject to the instability remains as an open question, but depending on the explosion energy and the mass and distriubution of CSM, the conversion of kinetic energy into light can produce some of the most luminous supernovae in the universe. This process might also be able to produce moderately luminous transients even from non-terminal eruptions or low-energy explosions. Because many of these non-termal eruption can repeat, because low-energy explosions can come from relatively low-mass stars, and because some of the resulting supernovae are extraordinarily luminous, CSM interaction may figure prominently in the vast array of unusual transients now being discovered by transient searches (and by LSST in the near future). The latter part of the talk will explore the diversity of different transients that may result from CSM interaction, including a discussion of several individual observed examples that illustrate some of the extremes in parameter space. I'll end with a discussion of two very famous and very peculiar astronomical objects, where a simple model of CSM interaction may help resolve some long-standing mysteries and paradoxes that have seen little progress in the last 30 years.