iPTF14hls, a bizarre supernova (or zombie star), continues to explode repeatedly. The first known one occurred in 1954, and several more recently within 11 weeks. One possible explanation (Pulsational Pair-Instability Supernovae), hypothesized by Daniel Kasen and discovered by Arcavi, Howell, and Birnstein, posits a star of enormous size (common shortly after the Big Bang, but rare now), so large and heavy that it creates antimatter (positrons) in its core, which would then trigger violent, periodic explosions.
