A Supernova Right Out Of ‘The Walking Dead’: This ‘Zombie’ Star Died 60 Years Ago But Kept On Resurrecting

A supernova typically signals the death of a star, extinguished in a massive explosion that’s sometimes brighter than even a whole galaxy, if only for an instant. Yet astronomers at the Las Cumbres Observatory (LCO), in Goleta, California, stumbled upon a supernova so unique and mystifying that it challenges everything we knew about dying stars.

What makes this exceptional supernova unlike any others is the fact that it survived its own extinction more than 60 years ago, only to reignite time and again over the course of half a century. Researchers are calling it a “zombie” star, since it exploded multiple times and managed to come back to life.

Moreover, it maintained its glare six times longer than usual, “characteristics that differ extensively from those of known supernovae,” explain the astronomers in a paper published Wednesday in the journal Nature.

This confounding supernova was first spotted on September 22, 2014, by a team of researchers from the Palomar Transient Factory. Back then, it seemed there wasn’t anything special about the find; it looked just like an ordinary supernova and didn’t raise any suspicions about its nonconformist nature. The team dubbed it iPTF14hls and classified it as a type II-P supernova (the most common type astronomers come across), then moved on to more exciting work.

But later, something amazing happened. Five months into the discovery, in February of 2015, LCO astronomers noticed that supernova iPTF14hls had become brighter than when it was originally observed, instead of fading like it was expected.

This is so cool! Space is fascinating! ‘Zombie' star won't die, even after explodinghttps://t.co/nrJ208Mz7h #zombiestar #nasa #superneat

— Catherine Rezabeck (@catrbaker) November 8, 2017

Study author Iair Arcavi, a NASA Einstein postdoctoral fellow at LCO and the University of California Santa Barbara (UCSB), initially believed they caught a glimpse of a closer star somewhere in The Milky Way, which looked brighter due to its proximity to Earth. But a deeper look into its light signature placed the mystery star in a far-off galaxy nearly 500 million light-years away from our planet.

One hundred days later, supernova iPTF14hls looked like it had just exploded in the previous month; two years after, it seemed to be no more than 60 days old, reports Space.com, indicating another explosion in the previous two months.

Overall, supernova iPTF14hls seems to have exploded at least five times in the past three years, as its spectrum grew dimmer and brighter with each observation. This remarkable supernova is still bright today, in 2017, although its fading glare (now at one-hundredth of its peak brightness) suggests it may be finally singing its swan song.

Arcavi discussed this astounding discovery in a LCO news release, which notes this relentless supernova is probably “the most massive stellar explosion ever seen” and that the “zombie” star that originated it was at least 50 times bigger than our Sun.

“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.”

The light supernova iPTF14hls emits was analyzed using an instrument specifically designed by Nick Konidaris, from the Carnegie Institution for Science, in Washington. The SED Machine, as it is called, revealed that iPTF14hls remained bright for more than 600 days, as opposed to regular type II-P supernovae, which fade after no more than 100 days.

Konidaris built the SED Machine to help facilitate the process of classifying supernovae, but as he points out in a Carnegie news release, he “never expected it would help us analyze an explosion as strange as this zombie star.”

Even more surprising are the records of the LCO archive, which show evidence of an explosion in the same location as iPTF14hls dating back to 1954. This suggests the “zombie” star survived the explosion more than 60 years ago and exploded anew in 2014.

Arcavi’s team infers this could be the very first example of a “Pulsational Pair Instability Supernova” ever detected: a massive star that can repeatedly become a supernova due to an overheated core that remains intact while the star’s outer layers are blown away in recurrent explosions.

Study co-author Andy Howell, also from LCO and UCSB, says the discovery of supernova iPTF14hls “is like finding a dinosaur still alive today.”

“These explosions were only expected to be seen in the early universe and should be extinct today,” Howell describes in the news release.

https://www.youtube.com/watch?v=EAtoaYtSHi4

[Featured Image by Kevin Carden/iStock]