The study of massive stars exploding as supernovae has seen a major breakthrough in recent years, with modern surveys making the detection and exploration of supernova explosions within a day of stellar core collapse possible. With its extremely wide field of view and mature infrastructure of integrated hardware, software and operations, the Zwicky Transient Facility (ZTF) has made such detections a matter of routine. The first hours and days of cosmic explosions reveal a plethora of new physics: from the physics of the energetic shock breakout flares, via measurement of the explosion energy and extending to extensive mapping of the exploding star parameters: its radius, surface composition, and evolutionary history. X-ray emission is predicted (and was observed in a single serendipitous case) from the brief shock breakout phase, and more extended emission may result from interaction of the SN ejecta with circumstellar material that we have shown often surrounds the exploding massive progenitors. The ability to survey wide sky areas rapidly and synchronously from ground (visible) and space (X-ray) promises very high scientific returns.