The Star That Won’t Stay Dead

Fagjun | Published 2017-11-13 08:06

There’s a star out there that’s been repeatedly imploding over a period of 50 years--but it just wouldn’t stay dead. This has led astronomers to question what they thought they knew about the life and death of stars.


Artist's impression of a supernova [Image by NASA's Goddard Space Flight Center/ESA/Hubble/L. Calcada]

 

 

Think of a movie franchise whose installments keep bombing and yet the franchise itself just won’t die. On a more cosmic scale, that’s what the supernova iPTF14hls is like. A supernova is an explosion that occurs when a star is in its death throes. When the star is out of its nuclear fuel, some of its mass goes to its core. Too much matter then begins to accumulate in the core, which causes the star to explode. This results in a bright supernova, which happens only to supermassive stars which are larger in size than the sun.

 

Stars explode only once--at least, that what we thought we knew. When astronomers began investigating iPTF14hls, however, they realized that it’s no ordinary supernova.



Repeated Explosions


Image by Arcavi et al. 2017, Nature, via POSS/DSS/Las Cumbres Observatory/S. Wilkinson/CarnegieScience.edu

 

 

When iPTF14hls was first detected in 2014, astronomers didn’t see anything remarkable or out of the ordinary about it. It was deemed to be a regular old Type II-P supernova, which is the most common type of supernova that astronomers detect. Usually, this type of supernova stays bright for around a hundred days.

 

However, iPTF14hls remained bright for more than 600. Data from 1954 also showed there had already been an explosion in the same exact location, meaning it’s likely that the supernova exploded then and exploded again in 2014. When researchers discovered the supernova, they thought that it was already about to fade away.

 

However, one of the astronauts observing the supernova and many others noticed that iPTF14hls began growing brighter over a span of five months after its discovery. At first, researchers thought that it was a supernova that was relatively close to Earth, thus appearing to be brighter. However, they soon found that the supernova actually belonged to a galaxy 500 million light years away from Earth.

 

Then, after a hundred days, researchers noticed that the supernova looked like it was just 30 days old. After two years, it looked like it was only 60 days old. More recently, researchers said that the supernova still looked quite bright, though it does appear to finally be fading. At present, it’s at about a tenth of its peak brightness.



Questions and Answers


A graph depicting iPTF14hls's fluctuations in brightness [Image by Las Cumbres Observatory/S. ​Wilkinson]

 

 

So is this normal supernova behavior? Definitely not. At this time, researchers find the supernova unpredictable. It may fade away, it may grow brighter again, or it may promptly disappear. "We are beyond the cutting-edge of models," said Iair Arcavi, one of the authors of a study on the supernova. Other astronomers, meanwhile, agree that they too don’t really know what’s going on with iPTF14hls. However, many are already working on finding an explanation for this weird occurrence.

 

One thing’s for sure: astronomers would have to revisit existing models of supernovae. While iPTF14hls may be an explainable anomaly, it’s also possible that this phenomenon may be more common in the universe than we thought. For now, all these questions need to wait to receive their answers.

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