Science

'Zombie' star won't die, even after exploding

'Zombie' star won't die, even after exploding”

The core can then pulse like this again and again, shedding material until it eventually collapses into a black hole.

At least, that is what's supposed to happen.

When a massive star, more than eight times the mass of our Sun, runs out of fuel to keep it shining, it ends its life in a dramatic explosion.

The supernova is still bright, and the team will continue to monitor it.

But, he noted, "This is one of those head-scratcher type of events".

The discovery was made by scientists working on the Intermediate Palomar Transient Factory, which uses a telescope near San Diego to survey the night sky for ephemeral events like supernovas. "A theory could explain some stuff, but there's a problem, and then another theory can explain this other thing, but then there's a problem", said Andy Howell, an astronomer at Las Cumbres Observatory and the University of California, Santa Barbara, who leads the Las Cumbres supernova team. As the light fades and the supernova expands, it becomes more transparent, which will enable the researchers to take a closer look. The event looked like a garden variety star well on its way toward oblivion. Typical supernovas (blue) fade after about 100 days.

The researchers quietly monitored iPTF14hls for the next two years, discussing their unusual sighting with a few select theorists in the hope that someone would have a clue about what they had found. Ideas emerged - the birth, during a supernova, of a magnetar giving off bright flashes called gamma ray bursts, perhaps, or a newly formed black hole swallowing the starry material around it - but nothing quite worked. But several months later astronomers at Las Cumbres Observatory saw something unprecedented: iPTF14hls was getting brighter again after fading.

In Garching, Nugent thought to check the historical record for evidence of precursor explosions from iPTF14hls's progenitor star. This "spectrum" contained all the signatures of a supernova. But even the best theories don't quite match what astronomers observed, so the origins of this supernova still remain something of a mystery. Arcavi is a NASA Einstein postdoctoral fellow at California's Las Cumbres Observatory. The nova hit five peaks of brightness before finally seeming to dwindle in summer 2016.

No supernova was visible during the more recent observation.

The star, which lies half a billion light years away, has exploded numerous times since 1954.

What's more, archival data revealed a 1954 explosion in the exact same location. Astronomers believe iPTF14hls experienced at least two explosions, 60 years apart. The result is something that looks like a big explosion, but it ultimately leaves the core of the star intact. But given what astronomers know about the frequency of supernovas, Arcavi put this possibility at no more than 5 percent.

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. "We've never seen such a supernova before, so ours would be the first candidate". So astronomers began extensive observations with telescopes on the ground and in space.

"This process can repeat every few years or every few decades", said Arcavi. "That allows us to get a fingerprint of the supernova", says Arcavi.

But even that model can't keep up with the truly freakish behavior of this supernova.

Computer resources at Berkeley Lab's National Energy Research Scientific Computing Center (NERSC) were used to locate the September 2014 star explosion. They analyzed the light of the explosion to study the material ejected and its speed. "So if it is the first pulsational pair-instability supernova, we need to figure out why it doesn't look exactly as expected". "Or it might not be that, in which case the theory needs to be something completely new". They might be underestimating the energy of PPISNs. They'll also be keeping an eye on the supernova, since Arcavi is by no means convinced it won't act up again. As Nugent and the other supernova researchers absorbed the details about the incredibly long supernova, they thought of a well-known theory developed by Woosley, the Santa Cruz theorist, and others.



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