Supernovae are the engines of the universe, pulling material out of the furnaces of stars and spewing it into their galaxies. As some of the most powerful explosions since the Big Bang, they influence not only the chemical but also mechanical evolution of the galaxies they inhabit. They induce star formation and produce the building blocks of planets, organisms, and ultimately, civilizations. Grasping the connections between the supernovae we observe and the stars that would have produced them is a critical piece of understanding this process.
Unfortunately, we rarely have the ability to observe the progenitor stars of supernovae directly; it is usually difficult to predict when a given star will explode and most are in galaxies too distant to allow observation of individual stars. Instead, we typically must leverage our understanding of the explosions themselves to reveal the nature of the stars that produced them. Using analytical and numerical calculations, it is possible to predict the supernovae from certain types of stars and work backwards.
We present a new model for previously elusive rapidly fading supernovae, which we believe are due to the core-collapse explosions of massive stars inside extended hydrogen-free envelopes or previously ejected mass shells. This model requires not only pre-explosion stellar radii of unprecedented size for hydrogen-free stars but also a lack of radioactive nickel, which is usually present in supernovae. We show our process from simple toy models to self-consistent explosions of stellar models and compare our results to existing rapidly fading supernovae. Understanding these unusual transients will shed light on the many possible ways stars behave shortly before death and also may be critical for understanding the population of core-collapse supernovae as a whole.
