Most supernovas tend to last several months at most. However, one explosion known as PS1-10adi was detected in 2010 and was monitored by telescopes in La Palma and Hawaii for the next several years, defying all but the wildest expectations. By way of comparison, a long-duration supernova called iPTF14hls has been observed for two years and the researchers’ initial reaction to iPTF14hls was, “Is this normal?”
Supernova PS1-10adi (Or Is It Even A Supernova?)
Because PS1-10adi resides in a galaxy with a supermassive black hole about 2.4 billion light-years from Earth and displays higher levels of energy and duration than are usually expected from a supernova, theorists have suggested that it could have been a star that was ripped apart while being consumed by the black hole. Others have suggested that PS1-10adi could have been hundreds of times more massive than our sun. A star only has to be eight times more massive than our sun to form a supernova at the end of its lifespan.
Scientists aim to learn more about this new type of explosion using data that upcoming facilities will be capable of collecting. Dr Erkki Kankare, a member of the School of Mathematics and Physics at Queen’s University and lead author of the study published in Nature Astronomy, said of the unexpected discovery:
“If these explosions are tidal disruption events – where a star gets sufficiently close to a supermassive black hole’s event horizon and is shredded by the strong gravitational forces – then its properties are such that it would be a brand new type of tidal disruption event. If they are supernova explosions then their properties are more extreme than we have ever observed before, and are likely connected to the central environments of the host galaxies.”
Supernova iPTF14hls was considered a fairly normal Type II-P supernova when it was discovered in 2014. Type II-P is the most normal type of supernova that astronomers see. However, an alert student named Zheng Chuen Wong noticed that it was gradually getting brighter over the course of five months. This didn’t match any textbook description of how supernovae normally work. He showed the data to Iair Arcavi, an astronomer at the University of California, Santa Barbara, who recalls telling the student, “That is very strange. Supernovae don’t do that.”
She went on to become the lead author on a study of Supernova iPTF14hls. Upon further study, the supernova turned out to be part of an irregular galaxy about 500 million light years from Earth. It looked remarkably young for its age. After two years, iPTF14hls displayed the same light signature and brightness as a normal 60-day-old supernova would. Three years after its discovery, iPTF14hls appears to be finally fading out, although Arcarvi says that they shouldn’t count on that from a supernova this weird: “Just to be clear, though, there is no existing model or theory that explains all of the observations we have” on this particular supernova.
These two explosions may cause scientists to rethink their theories on how supernovas happen, especially when more sensitive instruments that can detect similar explosions are built and researchers stay alert for anything that challenges their expectations. As astrophysicist Stanford Woosley of the University of California said of Supernova iPTF14hls, “It’s just a puzzle in the sky. That’s what we live for, what astronomers love.”