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Star Refuses to Die—Supernova Occurs Again and Again

S u m m a r y :
A star that refuses to die has captured the attention of astronomers since 2014—the supernova has lasted for over 3 years now. The findings are published in the journal Nature.

A Star that Says, “I Don’t Want to Die”

The unusual star is named iPTF14hls; it was discovered in 2014 by the Palomar Transient Factory. It stands out from others of its kind because the explosion of stars (events known as supernovas) are, normally, thought to occur only once, after which they die and remain dead. However, this star appears to have erupted repeatedly over the last 3 years, with 2 other explosions that might have happened earlier. iPTF14hls is just not sick and tired of dying—it keeps on doing it. This never-ending supernova might constitute the first example of a theory that purports antimatter is burned inside the core of a star.

“A supernova is supposed to be a one-time thing—the star explodes, it’s dead, it’s done, it can’t explode again,” says astrophysicist Iair Arcavi from the University of California, Santa Barbara. “It’s the weirdest supernova we’ve ever seen … It’s like the star that keeps on dying.”

Artist’s rendition of the supernova of a star that appears to have exploded several times before. Photo credits: NASA, ESA, G. BACON/STSCI.

Brighter After Death

iPTF14hls is situated in a galaxy found around 500 million light years away from us. Initially, it looked like your usual type 2 supernova: a star is supposed to end in explosions, in the aftermath of which it glows for around 100 days, and gradually dims out. Our weird, weird star, however, only got brighter with time: it appeared to be locked in irregular cycles of brightening and dimming. Arcavi and his colleagues report that the supernova was bright was over 600 days.

“That’s just unheard of,” says theoretical physicist Stanford Woosley from the University of California; he was, however, not involved in the discovery. “Ordinary supernovae don’t do that.”

Also, historical data from Palomar Observatory records a bright burst from 1954 in the same region of heaven where the star is located.

Historical data from 1954. Photo credits: S. WILKINSON/LCO, DSS, POSS.

The Star Remained Hot Throughout

Exploding stars will eject gas layers that slow down and cool, leading to their expansion. However, iPTF14hls did not display such a trait: rather, its outer layers of gas would not slow down, and it kept its high temperature of around 5,700° Celsius throughout. The researchers believe that its gas might have already gone through the slowing and cooling phase earlier, during another massive eruption that might have occurred between 2010 and 2014.

Whims & Caprices of iPTF14hls

Evidence for the theory that stars 100 times the mass of the sun can undergo several explosions (several deaths) has never been found before. As per the hypotheses, these stars reach extremely high temperatures that allow them to convert gamma rays into electrons and their antimatter counterparts (positrons), which would give them enough energy to protect them from collapsing under their own gravity.

Otherwise, when stars are devoid of this high energy, their core collapses and becomes hotter; this collapse can cause a partial explosion whereby the stars blow off great amounts of mass. Then, following the explosion, the electrons and positrons may transform back again into gamma rays, keeping the remnants of the stellar core together.

The stars would release much energy several times, and ultimately die in a supernova whose leftovers would collapse into a huge black hole. Again, however, iPTF14hls is different. While the theory says that the star should blow off all of its hydrogen in the initial explosion, iPTF14hls went on to emit hydrogen worth 50 times the mass of the sun in 2014. Moreover, the recent explosion has also released a considerable amount of energy.

An Imminent Death

Commenting on the findings, Woosley says that the most recent data will hopefully help them figure out which theory is real, or if they should formulate a new one to explain iPTF14hls.

But also, iPTF14hls might not be having much time left—after all, we all have to die, right? The latest data suggests that it will soon fade, says Arcavi. But then, nothing can be said for sure without additional data.

“I am not making any more predictions about this thing,” Arcavi says. “It surprised us every time.”

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