Remarkable 'zombie star' exploded, survived - and then kept on exploding

Remarkable 'zombie star' exploded, survived - and then kept on exploding

However, an worldwide team of researchers has discovered a star that exploded multiple times over a period of 50 years, a finding that challenges everything we know about the death of stars. The researchers were flabbergasted when they found that in 1954, another explosion was recorded in the exact same location as iPTF14hls.

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

What's more, the astronomers found that its brightness varied by as much as 50% on an irregular timescale, as if it was exploding over and over again. Several months later, LCO astronomers noticed something that they had never seen before - the supernova was growing brighter again after it had faded.

Las Cumbres, a global network of robotic telescopes, is still observing the star and its proceedings.

Astronomers continue to monitor the supernova, which remains bright three years after it was discovered.

In addition, the "zombie" star's brightness peaked five times, not once, which is typical for supernovas.

The findings are published in the journal Nature. The leading idea is that this may have been something of an imposter - an event that looks like a supernova, but doesn't ultimately lead to the destruction of a star.

"I don't think this changes the picture for your plain old vanilla Type II-P supernovae".

Normally, supernovae reach peak brightness before fading over around 100 days.

To learn more about the exploding star, the astronomers initially took its light and separated it into its component colors, known as taking spectra.

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"Six hundred days later, the spectrum looked like that of a 60-day-old supernova", Arcavi said.

"This supernova breaks everything we thought we knew about how they work", said the study's lead author Iair Arcavi, a NASA Einstein Postdoctoral Fellow at the University of California-Santa Barbara and Las Cumbres Observatory, in a press release.

Usually, when something explodes, that's it-it's done. Such a highly magnetized neutron star can shine brightly for around two years. Whatever this was looked like a Type II-P supernova in composition but didn't behave like one.

"I never expected it would help us analyze an explosion as odd as this zombie star", Konidaris said of his invention. Until, that is, an intern looked back at the data and saw something weird. They're pretty sure it's the same star - or else a very unlikely coincidence. As to whether or not it could brighten again, he says, "I'm not making any bets".

But a subsequent image of the galaxy in 1993 showed no sign of the supernova.

The object may be the first known example of a Pulsational Pair Instability Supernova.

What theorists do know is that massive stars typically go supernova when their cores run out of nuclear fuel.

The star would then act like someone shoveling snow and gradually shedding outerwear: As it became unstable, it would eject a layer of mass, which would make it stable again for a limited time before heat built up again. Daniel Kasen, co-author of the paper and an associate professor at the University of California, Berkeley said it describes a star "so massive and hot that it generated antimatter in its core". In such stars, temperature rises to dizzying levels, in excess of 3 billion C (5.4 billion F) in the core, causing oxygen - then heavier elements - to fuse, blowing off massive amounts of material and resetting the cycle. It would then collapse into a black hole.

No one's ever actually seen a PPI in action before, so this would be a big first. During this short period, however, supernovae emit as much energy as the Sun emits during its entire lifespan. This supernova may be something completely new.

There are other less viable explanations for the zombie star, but nothing that fits quite right. Though faint now, it's still shining, even though a normal supernova would have extinguished long ago. Stephen Hawking has recently said that he is now certain, "more than ever that we are not alone", and has warned against communications with aliens who have far superior intelligence then ours.

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