Institute for Advanced Study/Princeton University Joint Astrophysics Colloquium

The advent of wide-field synoptic imaging has re-invigorated the venerable field of time domain astronomy. Our framework of optical transients no longer has a wide six-magnitude luminosity "gap" between the brightest novae and faintest supernovae. Multiple new and distinct classes of very rare explosions have been uncovered just in the past few years. I review the surge of excitement (and debate) on the physics of these transients with unprecedented explosion signatures. "Gap transients" represent missing pieces in two fundamental pictures: the fate of massive stars and the evolution of compact binaries. Calcium-rich gap transients may even be the key to solving a long standing abundance problem in the intra-cluster medium. Two classes of gap transients are extremely red motivating a systematic exploration of the dynamic infrared dynamic sky. I will present new, mysterious discoveries of infrared transients from a Spitzer search that just began called SPIRITS. I will conclude with the next frontier in gap transients --- discovering elusive binary neutron star mergers, a goal which may soon be within reach with coordination between the next generation Zwicky Transient Facility and advanced gravitational wave interferometers. This search may literally be the 21st century gold rush!