Star remains alive after multiple supernova explosions

Discovery may be a completely new type of object.
By Laurel Kornfeld | Nov 10, 2017
Astronomers are puzzled by the discovery of a massive star that continues to shine after having undergone numerous supernova explosions.

Discovered in September 2014 by an international team of scientists in an astronomical survey known as the Palomar Transient Factory, a supernova designated as iPTF14his initially appeared ordinary until it was found brightening after having faded.

Turning to archival data, the researchers found records of previous supernova explosions in the same location in both 1954 and 2014.

Every one of the thousands of supernovae observed by scientists prior to this one marked the death of the original star.

Led by scientists at Las Cumbres Observatory (LCO) in California, the research team proceeded to obtain spectra of the supernova using the W.M. Keck Observatory on Mauna Kea, Hawaii.

"The spectra we obtained at Keck Observatory showed that this supernova looked like nothing we had ever seen before. This, after discovering nearly 5,000 supernovae in the last two decades," noted Peter Nugent, Senior Scientist and Division Deputy for Science Engagement at the Computational Research Division of Lawrence Berkeley National Laboratory.

"While the spectra bear a resemblance to normal hydrogen-rich core-collapse supernova explosions, they grew brighter and dimmer at least five times more slowly, stretching an event which normally lasts 100 days to over two years."

High-resolution images of the supernova's spectra were obtained via the Deep Imaging and Multi-Object Spectrograph (DEIMOS) on the Keck 2 telescope.

Using the Keck 1 Low Resolution Imaging Spectrometer (LRIS), scientists were able to measure the spectrum of the supernova's host galaxy.

They determined the precursor star was significantly larger than the Sun and at least 50 times more massive and that it had exploded many times over slightly more than 50 years.

The star's unusually high mass may be the reason it survived multiple explosions.

"According to this theory, it is possible that this was the result of a star so massive and hot that it generated anti-matter in its core. That would cause the star to go violently unstable, and undergo repeated bright eruptions over periods of years," said Daniel Kasen of UC Berkeley, who is also a scientist at the Lawrence Berkeley Lab.

Known as a "Pulsational Pair Instability Supernova," this type of explosion would have been common in the early universe but should not be occurring now.

Additionally, the supernova has released more energy than current theory says it should.

"This supernova breaks everything we thought we knew about how they work. It's the biggest puzzle I've encountered in almost a decade of studying stellar explosions," said Iair Arcavi, who is a NASA Einstein postdoctoral fellow at LCO and at the University of California at Santa Barbara.

Arcavi is lead author and both Nugent and Kasen are co-authors of a study on the discovery published in the journal Nature.

 

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