Scientists discover freaky star that refuses to die

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Because the star has exploded several times, it may not even fit the definition of a supernova.

A supernova is a momentary astronomical event, which takes place during the last stellar evolutionary stages of a massive star's life, whose dramatic and catastrophic destruction is marked by one ultimate very big explosion.

One of the weirder parts of this story is that most theoretical models predict that most of the hydrogen from the star should be eliminated after the initial explosion, which there should only be one explosion anyway, but there was a 2014 blast for the "zombie" star that contained a great amount of hydrogen. Knowing the full spectrum of stellar fates is crucial for understanding galactic evolution. It looked like any other star that had just died and violently burst apart. It could very well be the biggest stellar explosion that has ever been observed, which might explain its death-defying peculiarity. Several months later, LCO astronomers noticed something that they had never seen before - the supernova was growing brighter again after it had faded. "They don't know a damn thing about it". This causes an explosion that blows off the star's outer layers and leaves the core intact.

This star died as a Type II-P supernova in a galaxy 500 million light years away. Typically, they continue to shine for roughly 100 days and over time they begin to fade. Until, that is, an intern looked back at the data and saw something weird. Instead, the "zombie" star has lasted 600 days. So after 600 days, the supernova looked as if it was only 60 days old.

The mysterious object, iPTF14hls, was picked up in September 2014 by a wide-field camera astronomy survey.

The idea was first suggested in the 1960s, and explains how a star can have multiple supernova bursts without being destroyed.

The radiation pressure from gamma rays stops a star from collapsing under gravity. It then contracts, then explodes, in a halting heave-ho.

This process can repeat over decades before the star explodes one final time, collapsing in on itself and turning into a black hole. As the ejected shells run into one another, the explosions appear to us as temporary brightening and dimming, as in the light signature of iPTF14hls. Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star. "But your eye doesn't lie".

"So, if iPTF14hls is the first pulsational pair instability supernova then the theory needs to be revised". When such a star reaches the end of its life, its core can get incredibly hot - upwards of billions of degrees - and become unstable.


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

For one thing, the huge energy released in the course of iPTF14hls's known explosions (and there may have been more) already surpasses Woosley's predictions for how much energy the pair-instability mechanism can muster.

But there are a few problems with that theory: for one, this was only thought to happen in the early days of the universe. The fresh raw ingredients in dwarf galaxies allow huge stars to form, like pumpkins in fertile soil. After a long time shining, the supernova is now is fading to darkness. "Probably in the early universe these were much more common, but it's more or less extinct now", Howell said.

Now that iPTF14hls has been found and described, similar objects might start showing up. This supernova may be something completely new.

Using LCO's global telescope network, which is specifically designed for sustained observations, astronomers will continue to monitor iPTF14hls for changes in brightness over time.

These two images show the location of supernova iPTF14hls in 1954 and the absence of the supernova in 1993.

The fact that astronomers has spotted a supernova that has apparently "risen from the dead" is truly puzzling to science. "So they're not just wrinkles on an old theme; they are beasts". With this star, however, the materials around the event remained at really high speeds.

"It begs the question: how many have we missed in the past?" he said.

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