Astronomers have discovered the brightest supernova ever observed, which blasted out at least twice as much light as the next biggest star explosion on record.
First spotted on February 22, 2016 by the Pan-STARRS observatory in Hawaii, the gigantic detonation emitted the “largest radiated energy for any confirmed supernova,” according to a study published on Monday in Nature Astronomy. A team led by Matt Nicholl, an astronomer at the University of Birmingham, used multiple telescopes to examine the fallout of the explosion for two years, until it faded to a fraction of its peak brightness.
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“The earliest data from Pan-STARRS showed that this supernova was likely much brighter than the galaxy in which it exploded, so this immediately brought it to our attention as something that might be interesting,” Nicholl said in an email.
The event, known as SN2016aps, belongs to a special category of star explosion called superluminous supernovae, which have only been observed twice before. Scientists think that these superluminous events are the death rattles of gargantuan stars with masses at least 40 times that of the Sun. By comparison, “regular” supernovae are produced by stars with only a quarter of that heft.
Following the first detection with Pan-STARRs, Nicholl and his colleagues calculated that the explosion originated in a small galaxy about 4.6 billion light years from Earth. The extreme brightness of the supernova, even at such an immense distance, tipped the team off to its record-breaking nature.
“We knew it was important, because the luminosity at the time of discovery was up there with any supernova that had been seen before,” Nicholl said. “This prompted us to follow up on the detection, but it was only a few months later when we saw that it was fading away so slowly that we realised it was a very important and special supernova.”
“This is because being both very bright and long-lived means that the total energy (and very likely the mass of the star) had to be huge,” he added.
Indeed, the star that blew up into SN2016aps may have been anywhere from 50 to 100 times more massive than the Sun, according to the team’s models. The object may even have been a binary star system that eventually merged into a single stellar object, which then erupted into this supernova.
Regardless of how it evolved during its lifetime, this star’s death offers an unprecedented glimpse of the brilliant swan songs of unusually massive stars. The sheer radiance of SN2016aps suggests it was likely an example of a mysterious phenomenon known as a pulsational pair-instability, which would explain its enormous energy output.
During the leadup to its final fatal blast, the star was probably rocked by pulsations, causing it to shed a huge shell of gas. When the star subsequently erupted in a full supernova, the blast caught up to the shedded shell, torching the gas in a way that “sets SN2016aps apart from all previous events,” according to the study.
The discovery not only explodes records set by previous outbursts, it also provides a roadmap to detecting more of these superluminous supernovae created by massive stars. Scientists think that these enormous stars were more common in the early universe, so SN2016aps could shine an important light into this mysterious period in cosmic history.
Fortunately, next-generation telescopes such as the Vera C. Rubin Observatory in Chile and NASA’s James Webb Space Telescope may be able to scan for such explosions across several billion light years.
“We might actually be able to see the very first stars if they explode in a similar manner to this one, now we know what to look for,” Nicholl said. “Determining whether such massive stars and explosions were more prevalent in the early universe will help us to understand how they shaped the dynamics and chemical compositions of the galaxies we see today.”
