A star that never dies. An international team of astronomers that included experts Nick Konidaris and Benjamin Shappee from Carnegie Mellon University (USA) has discovered a star that exploded several times in a period of 50 years without disappearing in these events. The finding, published by Nature , completely confuses our existing knowledge about the end of a star’s life through a supernova.
Usually when a star goes supernova, that is where it ends. Is the end. However, this new discovery could change the way we see the death of stars as this one, called iPTF14hls, became a supernova; then it was lit up again and, some 60 years later, it went supernova again. How is it possible?
At first it was classified as a type II-P supernova – it looked like any other known supernova. In fact, the spectroscopic characteristics of the iPTF14hls supernova were identical to those of a type II- P supernova. But, to the surprise of astronomers, several months later, it did something supernovae don’t usually do: it glowed again.
After 600 days of observation, it dimmed and brightened several times , at least five times in less than three years. Supernovae typically peak at their brightness, glow for a few months, and then continually darken.
When scientists re-examined the archival data, they found something surprising: The star had already exploded in a type II-P supernova in 1954 .
“This supernova breaks with everything we thought we knew about how supernovae work,” says Iair Arcavi of the Las Cumbres Observatory and leader of the work. “It’s the biggest puzzle I’ve found in nearly a decade of studying stellar explosions .”
According to data published in the journal Nature, the original star was large, at least 50 times more massive than the Sun, and probably much larger. “The iPTF14hls supernova may be the most massive stellar explosion ever seen,” says Lars Bildsten, co-author of the work.
A possible explanation to the enigma
The researchers believe that it is an unstable supernova pulsation, something that had never been observed before , so it would be the first phenomenon of its kind in the history of astronomy, something that is believed to have happened to the star Eta Carinae A in 1843. But it is only a hypothesis.
This event appears to be a supernova that does not destroy its host star , and generally occurs in stars with around 95 to 130 solar masses. Supernovae would continue to occur until the star finally collapsed into a black hole.
“ This type of event should have been common at the beginning of the universe, but not today. It is almost like finding a living dinosaur today. If it happens to you, the normal thing is that you wonder if it really is a dinosaur”, explains Andy Howell, co-author of the study.
However, there is a problem with that hypothesis . The unstable supernova pulsation model does not account for the continued presence of hydrogen. iPTF14hls held too much hydrogen to adjust to a pulse. Also, the most recent explosion of the star used more energy than this model can represent. Which means that either iPTF14hls is such a weird but really weird supernova, or something completely new.
The team continues to monitor the supernova in the hope that the answer will eventually clear up.
Reference: Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star, Nature (2017). nature.com/articles/doi:10.1038/nature24030
