A shocking supernova refuses to die.
This exploding star, named iPTF14hls, has erupted continuously for the last three years, and it may have had two other outbursts in the past, astronomers report in the Nov. 9 Nature. Such a tireless supernova could be the first example of a proposed explosion that involves burning antimatter in a stellar core — or it could be something new altogether.
“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 of the University of California, Santa Barbara. “It’s the weirdest supernova we’ve ever seen … It’s like the star that keeps on dying.”
When iPTF14hls was discovered in September 2014 by the Intermediate Palomar Transient Factory, which scans the sky regularly with a telescope at the Palomar Observatory near San Diego, it looked like an ordinary type 2 supernova in a galaxy about 500 million light-years away. These explosions mark the death throes of a star between eight and about 50 times the mass of the sun (SN: 2/18/17, p. 24), and typically glow for about 100 days before starting to dim.
The first sign that iPTF14hls was unusual came a few weeks after its discovery, when it started growing brighter. That turned out to be one of five irregular cycles of brightening and dimming.
Even stranger, data collected from September 2014 to June 2016 show that the supernova remained bright for more than 600 days, Arcavi and colleagues report. The eruption, which is just showing signs of winding down now, may have already been in progress when it was discovered, so it could have persisted even longer.
“That’s just unheard of,” says theoretical physicist Stanford Woosley of the University of California, Santa Cruz, who was not involved in the discovery. “Ordinary supernovae don’t do that.”
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