Discovery of ‘zombie’ supernova like finding a dinosaur alive today

9 Nov 2017

Image: Allexxandar/Shutterstock

The fact that astronomers have spotted a supernova that has apparently ‘risen from the dead’ is truly puzzling to science.

Astronomers have seen their fair share of supernovae over the past few decades, but a particular one in the distant cosmos has mystified a team from UC Santa Barbara.

Unlike all the exploding stars we have seen before, the researchers were astonished to find that supernova iPTF14hls has exploded not once, but twice.

By searching through the archives, the team found that in that exact location of space, a star had exploded in 1954, but somehow it survived that explosion to erupt again in 2014.

Calculations suggest that the star was at least 50 times bigger than our sun, but probably even larger.

“This​ ​supernova​ ​breaks everything​ ​we​ ​thought​ ​we​ ​knew​ ​about​ ​how​ ​they​ ​work,” said lead author Iair Arcavi. “It’s​ ​the​ ​biggest​ ​puzzle​ ​I’ve encountered​ ​in​ ​almost​ ​a​ ​decade​ ​of​ ​studying​ ​stellar​ ​explosions.”

What made it stand out

What first caught the attention of Arcavi and his team was that, while iPTF14hls looked like any other supernova when it was observed in 2014, several months later, it appeared that the fading giant was getting brighter.

A typical supernova’s brightness dissipates over a period of 100 days, but this unique find was getting brighter and dimmer over a period of three years.

“Supernova​ ​iPTF14hls​ ​may​ ​be​ ​the​ ​most massive​ ​stellar​ ​explosion​ ​ever​ ​seen,” explained co-author Lars Bildsten.

“For me, the most remarkable aspect of this supernova was its long duration, something we have never seen before. It certainly puzzled all of us as it just continued shining.”

Like looking back in time

The discovery isn’t completely unprecedented, however, as it could be the first example of a​ ​pulsational​ ​pair​-instability supernova.​ ​

It has been theorised that the cores of massive​ ​stars​ ​become​ ​so​ ​hot​ ​that energy​ ​is​ ​converted​ ​into​ ​matter​ ​and​ ​antimatter.​ ​This​ ​causes​ ​an​ ​explosion​ ​that blows​ ​off​ ​the​ ​star’s outer​ ​layers​ ​and​ ​leaves​ ​the​ ​core​ ​intact. The process can then repeat over a period of decades until a final explosion leaves a black hole.

“These​ ​explosions​ ​were​ ​only​ ​expected​ ​to​ ​be​ ​seen​ ​in​ ​the​ ​early​ ​universe ​and​ ​should​ ​be extinct​ ​today,” said co-author Andy Howell.

“This​ ​is​ ​like​ ​finding​ ​a​ ​dinosaur​ ​still​ ​alive​ ​today.​ ​If​ ​you​ ​found​ ​one,​ ​you would​ ​question​ ​whether​ ​it​ ​truly​ ​was​ ​a​ ​dinosaur.”

The team’s research is published in Nature.

Colm Gorey was a senior journalist with Silicon Republic