A supernova is the explosive death of a massive star. Following the bright explosion, which can often be seen at vast distances across the universe, only a neutron star or black hole is left.At least, usually.Last November, astronomers made a stunning announcement: They'd found a star that had cheated death . This strange "zombie star" has been observed going supernova twice, once in 1954 and again in 2014. It is the first such object of its kind ever discovered.The star's name is iPTF14hls, and its behavior has been called "the biggest puzzle I’ve encountered" by Iair Arcavi, lead author of the discovery paper. What's going on here? To dig deeper into the puzzle behind this mysterious star, The Kavli Foundation recently hosted a roundtable discussion with several experts in the field, and generously shared the result with Astronomy magazine, republished below.Ordinarily, a supernova marks the death of a mammoth star, which then briefly outshines an entire galaxy before fading away. Not so for a baffling supernova that went off in a nearby galaxy in 2014. Instead of being the end of the story, the stellar explosion inexplicably began to brighten and has since dimmed, then brightened up again four more times.If that weren't odd enough, it turns out a supernova blew up in the same place in the sky more than 60 years ago. Somehow, a star that apparently died around the time Elvis Presley released his first record endured only to die again—truly a “living dead” star.Astrophysicists suspect this apparent stellar zombie was a rare, colossal type of star with 50 to 100 times the mass of our Sun. The universe’s first stars were similarly huge, they think, though these distant objects lie beyond the reach of even our most powerful telescopes. The re-exploding star could, therefore, be a cosmic anachronism, offering scientists an unprecedented glimpse into the primeval universe.To discuss the major scientific potential of this supernova, The Kavli Foundation reached out to two scientists key to its discovery, as well as an astrophysicist who specializes in massive stars.The participants were:– is an observational astronomer and NASA Einstein Postdoctoral Fellow at the University of California, Santa Barbara (UCSB) and the Las Cumbres Observatory , as well as a former researcher at the Kavli Institute for Theoretical Physics (KITP) . He is the lead author of a Nature paper describing the strange supernova.– is the Director of KITP and a Professor in the Physics Department at UCSB. A co-author of the new paper, Bildsten’s specialty is developing theories that explain supernovae.– is an Assistant Professor of Astronomy at the University of Washington . Her research focuses on massive stars, such as the one implicated in this re-exploding supernova.The following is an edited transcript of their roundtable discussion. The participants have been provided the opportunity to amend or edit their remarks.Most supernovae get bright over a few days or weeks, then fainter over a few weeks and months, and then they disappear and we never see them again. This supernova has gone bright-faint, bright-faint about five times over the course of three years! We’ve never seen that before.Another weird thing is when we took a spectrum, or fingerprint, of this supernova, which is useful for identifying what type it is, we got very ordinary results. Despite the supernovae’s strange behavior, the spectrum matched that of the most typical supernovae, which have a lot of hydrogen in them. We’ve seen hundreds of those. A normal spectrum was the last thing we were expecting to see.The third puzzling thing: We found this photographic plate from 1954 with an image of this supernova’s host galaxy, and we can see a supernova going off at the same position. We’ve never seen the same place in the sky explode twice before—let alone 60 years apart.