Every massive star experiences last stellar evolutionary stages, thus, going supernova. However, this strange star went supernova more than once.

Astronomers have observed supernovae thousands of times. Every explosion has been considered to be the terminal explosion of a star.

Until now, we have known that when a massive star blows itself up, it should remain dead. However, this is not the same for this weird supernova star which astronomers have named it iPTF14hls.

This is the first time for astronomers, to discover a star that has gone supernova more than once.

The Palomar Transient Factory, a fully automated, wide-field survey designed to spot cosmic objects that vary in brightness over time, discovered iPTF14hls in September 2014. Firstly, astronomers thought they were just looking at an ordinary supernova. But several months later, LCO astronomers noticed something that they had never seen before. The supernova was growing brighter again after it had faded.

Usually, after a normal supernova reaches the peak brightness, it fades over approximately 100 days. But supernova iPTF14hls, on the other hand, grew brighter and dimmer at least five times over two years.

Over the course of two years, iPTF14hls grew and dropped in brightness at least five times. Most supernovae remain bright for around 100 days before fading for good. Credit: LCO/S. Wilkinson

After discovering this weird feature, researchers decided to go back and search for archival data. They found another explosion recorded in the exact same location as iPTF14hls and it baffled them. Basically, this star somehow survived that explosion and exploded again in 2014.

The journal Nature published this work on November 8. Iair Arcavi, a NASA Einstein postdoctoral fellow at LCO and the University of California, Santa Barbara, led the study. Dr. Arcavi said, “This supernova breaks everything we thought we knew about how they work. It’s the biggest puzzle I’ve encountered in almost a decade of studying stellar explosions.”

So, this event is challenging many of the existing theories about how massive stars end their lives.

Is there an explanation for this event?

One theory is that the “zombie star” is actually a “pulsation pair-instability supernova.”

“According to this theory, it is possible that this was the result of a star so massive and hot that it generated antimatter in its core,” said co-author Daniel Kasen, a professor of physics and astronomy at the University of California-Berkeley. “That would cause the star to go violently unstable, and undergo repeated bright eruptions over periods of years.” The authors of the study calculated that before the first explosion, the star was at least 50 times as massive as the Sun (and likely larger).

Andy Howell, the leader of the LCO supernova group and a co-author of the study, said “These explosions were only expected to be seen in the early universe and should be extinct today. This is like finding a dinosaur still alive today. If you found one, you would question whether it truly was a dinosaur.”

Thumbnail Image: Artist’s concept of a supernova, an expanding shell of dust and gas is blown outward, away from the star’s dense, white-dwarf core. Credit: NASA/ESA/STSCI/G. Bacon