July 22, 2018

'Bizarre star that refuses to die discovered'

12 November 2017, 02:26 | Rodolfo Wallace

'Bizarre star that refuses to die discovered'

This artist’s impression shows dust forming around a supernova explosion. Astronomers have found a star that has exploded multiple times over 60 years something never seen before

Supernovae, the explosions of stars, have been observed in the thousands and in all cases they marked the death of a star. "It's the biggest puzzle I've encountered in nearly a decade of studying stellar explosions", said co-author Iair Arcavi, a postdoctoral fellow at Las Cumbres Observatory (LCO) who is based in California.

The "zombie" star kept erupting for almost two years - six times longer than the duration of a typical supernova.

The supernova, named iPTF14hls, was discovered in September of 2014 by the Palomar Transient Factory.

"This supernova breaks everything we thought we knew about how they work".

Though the star was discovered three years ago, once astronomers realized its freakish behaviour, they consulted archival data and discovered that an explosion happened in the same spot - about half-a-billion light years away from Earth - 50 years ago.

When the worldwide team of astronomers first spotted the explosion, a spectral analysis indicated it was just a run-of-the-mill, Type II-P supernova whose brightness would likely fade after about 100 days.

"This [was] one of those head-scratcher type of events", said co-author Peter Nugent, a senior scientist at Lawrence Berkeley National Laboratory.

It's the celestial equivalent of a horror film adversary: a star that just wouldn't stay dead.

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Astronomers identified it as an exploding star in January 2015; everything about the discovery seemed normal at first. The researchers were flabbergasted when they found that in 1954, another explosion was recorded in the exact same location as iPTF14hls.

Astronomy Now claims that supernova iPTF14hls could be the first example of what is called "pulsational pair instability supernova". This theory holds that massive stars become so hot in their cores that energy is converted into matter and antimatter.

"That would cause the star to go violently unstable, and undergo repeated bright eruptions over periods of years".

A study revealed that the star which exploded was at least 50 times more massive than the Sun and probably even much larger than that.

Leader of the LCO supernova group, Andy Howell, said such explosions were visible only in the early universe and should have not existed this long. "If you found one, you would question whether it truly was a dinosaur".

Writing in a news and views article published in Nature, Prof Stan Woosley, from the University of California, Santa Cruz, said that in the Pulsational Pair Instability theory, a massive star may lose about half its mass before the series of violent pulses begins.

LCO claims it is monitoring the supernova every few days for several years using the global telescope network as long-term observation is essential to study unusual events like this. "I can't wait to see what we'll continue to find by looking at the sky in the new ways that only LCO can afford us".

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