Ground telescope finds ‘zombie star’ that refuses to die
Astronomers are amazed to find a supernova isn't playing by the rules – getting brighter rather than fading away
Long-held wisdom that supernovae shine for months as they explode has been turned on its head following the discovery of a ‘zombie star’ that's still shining bright years later. Astronomers at Las Cumbres Observatory, California have been startled to discover that the supernova known as iPTF14hls has not merely peaked and faded over the course of 100 days as expected, but has actually been growing dimmer and brighter for two years.
Scientists are now seeking to confirm and explain the observation which, as it stands, defies their understanding of how stars evolve and die. First detected on 22 September 2014 by a telescope in
San Diego, it appeared to be a typical example of a Type II-P supernova, but, five months later, they noticed that it had become brighter. What's more, after two years it looked like it was just 60-days old, and it remains bright to this day.
“The supernova offers astronomers their greatest thrill: something they do not understand,” says Stan Woosley, director of the Center for Supernova Research at the University of California, Santa Cruz. Certainly there is no existing model or theory to explain the observation, and scientists are not even sure what will happen next. It could fade, grow brighter or suddenly disappear, but what is even more intriguing is that the supernova – which is 500-million-light-years from Earth in the constellation Ursa Major – is in the same spot as another supernova spotted in 1954. There's a 95 to 99 per cent possibility that the supernova has been undergoing this event for at least 63 years.
But even that is not the end of it. Woosley says the supernova has varied in brightness by as much as 50 per cent, so it could be going through a cycle of exploding, fading and exploding again. One potential explanation is the ‘pulsational pairinstability model’ which states a star with a mass of more than 100 Suns is able to explode multiple times before dying. Blasts send material rushing from the star and it can collide with older material, producing a bright flash of light.
Woosley says the model isn't able to account for the huge amount of energy released by iPTF14hls, though. There is also no observation of this model in action, so no-one knows for certain if it does exist. In the meantime, scientists have moved to using larger instruments as they continue to monitor the supernova. They are also seeking to look at it with the Hubble Space Telescope in a bid to shed more light on the mystery.
“The supernova offers astronomers their greatest thrill: something they do not understand”