Mauna Kea telescope details rare supernova

A supernova, by definition, is a star that explodes into oblivion, a spectacular and final plunge into the throes of death.

But now an international team of astronomers, armed with data partly gained from the Keck Observatory on Mauna Kea, has announced the remarkable discovery of a supernova that refuses to bite the cosmic dust.

It’s essentially a zombie star.

The team, led by the Las Cumbres Observatory in California, reported this month in a study in the journal Nature that a distant star has exploded multiple times over a period of more than 50 years — a discovery that challenges what scientists thought they knew about supernova.

“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,” study co-author Peter Nugent of the Lawrence Berkeley National Laboratory said in a release.

While pictures of the star 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 that normally lasts 14 weeks to over two years, Nugent said.

Researchers used a spectrometer on the Keck I telescope to obtain spectrum pictures of the star’s host galaxy, while a spectrograph on Keck II captured high-­resolution spectra of the unusual star itself.

When the star was first seen exploding in 2014, it looked like your average supernova.

But a few months later, astronomers at Las Cumbres Observatory saw it getting brighter. They’ve seen it grow faint, then bright, then faint again five times. They’ve even found past evidence of an explosion 60 years earlier at the same spot.

Supernovas typically fade over 100 days. This one is still going strong after 1,000 days, although it’s gradually fading.

“It’s very surprising and very exciting,” said astrophysicist Iair Arcavi of the University of California, Santa Barbara, who led the study. “We thought we’ve seen everything there is to see in supernovae after seeing so many of them, but you always get surprised by the universe. This one just really blew away everything we thought we understood about them.”

The supernova — officially known as iPTF14hls — is believed to have once been a star up to 100 times more massive than our sun. It could well be the biggest stellar explosion ever observed, which might explain its death-defying peculiarity.

It could be multiple explosions occurring so frequently that they run into one another or perhaps a single explosion that repeatedly gets brighter and fainter, though scientists don’t know exactly how this happens.

One possibility is that this star was so massive, and its core so hot, that an explosion blew away the outer layers and left the center intact enough to repeat the entire process. But this pulsating-star theory still doesn’t explain everything about this supernova, Arcavi said.

Harvard University’s astronomy chairman, Avi Loeb, who was not involved in the study, speculates a black hole or magnetar — a neutron star with a strong magnetic field — might be at the center of this never-before-seen behavior. Further monitoring might better explain what’s going on, he said.

Las Cumbres, a global network of robotic telescopes, continues to keep watch.

Scientists do not know whether this particular supernova is unique; it appears rare since no others have been detected.

“We could actually have missed plenty of them because it kind of masquerades as a normal supernova if you only look at it once,” Arcavi said.

Nothing lasts forever — not even this super supernova.

“Eventually, this star will go out at some point,” Arcavi said. “I mean, energy has to run out eventually.”