Scientists have snagged the earliest observations of a supernova ever captured, taken only three hours after a dying star began its fatally explosive finale. The research, published Monday in Nature Physics, opens a new window into the leadup and immediate fallout of stellar self-detonation, information that is normally blown into oblivion before astronomers have a chance to study it.
"There's a limited time window," said study author Ofer Yaron, an astrophysicist based at the Weizmann Institute of Science in Israel, in a Skype interview with Motherboard. Within days, he said, supernova ejecta traveling at the incredible velocity of 10,000 kilometers per second engulf the regions surrounding exploding stars, destroying evidence of the initial collapse.
But this particular supernova, called SN 2013fs, was spotted early on October 6, 2013 by the California-based Intermediate Palomar Transient Factory (iPTF). This wide-field sky survey operates in real time to detect flashy transient phenomenon and trigger follow-up observations over a network of facilities around the world.
Located in the galaxy NGC 7610, about 160 million light years from the Milky Way, SN 2013fs was flagged by iPTF swiftly enough for scientists to glimpse the dense disk of circumstellar material kicked off by the star during its death rattles. (Scientists observed light from the young supernova arriving at Earth; the event itself occurred over 100 million years ago.)
SN 2013fs is a type II supernova, which means its progenitor star was likely a red supergiant at least ten times as massive as the Sun. Though scientists understand in broad strokes how these massive stars wind down their lives, the finer details of their pre-explosion mass loss and its resulting impact on the stars' final core collapse remains poorly understood.
"Those are the earliest spectra ever taken of a supernova explosion," Yaron told me. "It's from those early spectra that we managed to learn so much about the distribution of the material that we found to exist around this exploding supernova."
Indeed, Yaron and his colleagues were able to witness the explosion's shockwave as it briefly ionized the shell of dense stellar material encircling the ailing star. Emission spectra from this event indicated that the supergiant had been shedding its star stuff for several hundreds of days prior to collapse, and gave the team confined parameters for understanding this key process.
"Before going supernova, the star experiences very significant instabilities in its interior, affecting the outer envelopes and surface, which causes this elevated, maybe even eruptive, mass loss, just before the explosion," Yaron said.
"It's as if the star knows that it is finishing its life soon, that it will die soon, and it puffs some material outside in its last breaths," he continued. "It's like volcanoes or geysers where, in many cases, you will see some bubbling of material and ejection of lava on a smaller scale before the real eruption. Studies like this strengthen our understanding of the very final stages of massive stars, showing that [are] hints of the coming supernova explosion."
Fortunately for those interested in the swan songs of massive stars—and who in their right mind isn't?—these kinds of early detections will become more frequent as more sophisticated sky surveys are debuted in the future. For instance, the iPTF survey will be replaced later in 2017 by the Zwicky Transient Facility (ZTF) survey, which will be capable of scanning 3,750 square degrees of space an hour, amounting to almost the entire visible sky, within one night of observations.
"This really opens up possibilities," Yaron said. "There will be many more transients detected per night, many more supernovae, and among those, many supernovae that will be detected early, like this specific case."
"We already managed to decrease the timescales of detections to hours instead of days, as it used to be in the past. Now really the aim is to even lower this down to the minutes timescales from the explosions themselves."
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