In the first part of this talk I will describe how type 1a supernovae (SN) can be used to constrain the interactions of heavy dark matter (DM), which may heat a white dwarf (WD) sufficient to trigger runaway fusion and ignite a SN. Based on the existence of long-lived WDs and the observed supernovae rate, we constrain ultra-heavy DM candidates that produce high energy SM particles in a WD. This rules out supersymmetric Q-ball DM in parameter space complementary to terrestrial bounds. We also constrain DM which is captured by WDs and forms a self-gravitating DM core. Such a core may form a black hole that ignites a SN via Hawking radiation, or which causes ignition via a burst of annihilation during gravitational collapse. It is intriguing that these DM-induced ignition scenarios provide an alternative mechanism of triggering SN from sub-Chandrasekhar mass progenitors. In the second part of the talk, I will present a new technique which utilizes superconducting RF cavities to significantly improve the sensitivity of "light shinning through walls" searches for axion-like particles (ALPs). Our design uses a gapped toroid to confine the static magnetic field responsible for axion-photon conversion, and thereby prevent quenching of the superconducting cavities . Such a search has the potential to probe axion-photon couplings to g ~ 2 x 10^-11 GeV^-1, comparable to future optical and solar searches.