| Abstract: | Type Ia supernovae (SNe Ia) have been celebrated for their use as standardizable candles and their central role in the discovery and exploration of dark energy. And yet, we have still not been able to determine exactly what type of star system explodes as a Type Ia supernova, or how the explosion itself occurs. In my talk, I will show how the last visible light from SNe Ia more than 1000 days after explosion can be used as a new diagnostic to constrain progenitor and explosion models. Using the Hubble Space Telescope, we followed several nearby SNe Ia and showed that their light curves, which until then were powered solely by the radioactive decay of 56Co, began to slow down. The exact reason for this slow-down is still in debate, but may be solved by a new "Phillips-like" correlation observed between the shape of the late-time light curve and the intrinsic luminosity of the SNe. |