But there are limitations to this explanation. iPTF14hls produced far more energy than the theory predicts it should. Arcavi said every scientist to whom he’s shown the findings is stumped. “And still now, even with the paper being published, we still don’t have any theory or any model that fully explains the observations of it,” he said. It even took some convincing for Nature to publish a paper that didn’t have a concrete answer for such a significant conundrum, he said. But to truly explain the supernova, astronomers around the world need to see the data and come up with a completely new model. Perhaps someone will even discover earlier images of the supernova in their own archival data, Arcavi said.
Sarah Sadavoy, an astronomer at the Smithsonian Astrophysical Observatory at Harvard University who was not involved in the study, called the long-lasting supernova a “strange event.” The biggest mystery in the findings, she said, is the detection of hydrogen at the scene of the cosmic explosion. “Hydrogen is found in the outermost layer of these massive stars, and as such, should be lost during the first burst,” Sarah said. “This particular event is just as powerful as most other supernova of this type, so it doesn’t make sense for it to still have hydrogen.”
But cosmic mysteries, while frustrating, are a good thing. “There are many things that we still don’t understand about the explosion mechanisms of massive stars and the associated element production,” said Anna Frebel, an astrophysicist at the Massachusetts Institute of Technology who studies stars. “Finding this object appears to cause more puzzling ‘problems’ since it’s never been seen before, but it’s those kind of challenges that help astronomers understand more about the death of stars.”
Arcavi said the discovery will force astronomers to reexamine the supernovae they’ve encountered in their observations. “Anytime someone reports a supernova of this type, we have to look at it again and check if it’s not one of these weird ones,” he said. “We don’t know how many of these we might have missed.”
Some researchers are calling the star responsible for iPTF14hls a zombie star, an undead being glowing in the cosmos. Arcavi said he has some mixed feelings about the nickname. The Walking Dead and many other depictions of the undead have shown that zombies, after considerable effort, can be killed. And when they’re dead, they usually stay dead, save for, perhaps, one final gasp when the unlucky human who took it out has turned away. This star, on the hand, won’t stop dying.
The supernova has begun to fade slowly in the last year, however. Astronomers hope that as the ejected material expands, the area may become transparent enough for powerful telescopes to glimpse the heart of the explosion. Hubble, the premier star-observing space telescope, will take a look next month. The future of iPTF14hls is unclear. Arcavi and his colleagues don’t know whether the star survived the explosion.
“It is weird that the current explosion is going on for so long, but that doesn’t necessarily mean that the star is still alive,” Arcavi said. “I wouldn’t bet my car on it either way.”