Astronomers are discovering an increasing number of peculiar supernovae, including a class of brilliant (though rare) ultra-luminous optical transients, some 100 times brighter than ordinary core collapse events. What powers these phenomenal displays is unclear, and poses one of the more interesting open questions in the study of stellar explosions. I will argue, based on simple theory and numerical simulations, that some of the ultra-luminous supernovae are not powered by the ordinary mechanism of radioactive decay I will then go on to discuss models in which the luminosity is boosted by an internal engine formed when the central core collapses -- either a rapidly rotating, highly magnetized neutron star, or a black hole accreting whatever material failed to escape in the supernova explosion.
Prof. Kasen's interests are in theoretical and computational astrophysics, with an emphasis on supernovae and other energetic transients. He uses multi-dimensional supercomputer simulations to study astronomical explosions and their applicability as probes of cosmology and fundamental physics. More generally, he is interested in radiation transport across a range of astrophysical environments, from galaxies to extrasolar planets.