A supernova, by definition, is the final collapse and explosion of a supermassive star. This is the most violent event in the universe, as a star literally tears itself apart, only leaving behind its dense core with a nebula rich enough to forge new elements in the universe. Here’s our question: have we (humanity) ever witnessed a supernova before? Not really! Until recently, a team of astronomers observing a red supergiant star claimed to have witnessed a supermassive supernova. What they are trying to say here is that they saw a cosmic explosion. Kaboom!
Related media: Red Supergiant Star Goes Supernova
Have You Seen A SuperNova?
For the first time, astronomers have captured the final moment of the life of a red supergiant star — as they witnessed the massive beast tear itself in its final death throes before collapsing into a type II supernova. The new observation was published in the Astrophysical Journal was led by researchers from Northwestern University and the University of California at Berkeley (UC Berkeley). The team made this observation in the supergiant’s last 130 days leading up to its detonation.
This new observation debunked previous ideas of how red supergiants undergo right before going supernova. From earlier observations, it was thought that red supergiants were quiescent upon their detonation — there was no evidence of violent activities, neither eruption nor luminosity. In their new observation, they detected luminous radiation from a red supergiant final year before detonating. This suggests that, at least, supergiants undergo significant changes within their internal structure before they go kaboom.
“This is a breakthrough in our understanding of what massive stars do moments before they die,” says Wynn Jacobson-Galán, a former graduate research fellow of the National Science Foundation, now at UC Berkeley, and the study’s lead author. “Direct detection of pre-supernova activity in a red supergiant star has never been observed before in an ordinary type II supernova. For the first time, we watched a red supergiant star explode.”
When Goes The Nova?
The observation was conducted by members of Northwestern’s Center for Interdisciplinary and Exploratory Research in Astrophysics (CIERA), where Jacobson-Galán led the study before leaving for UC Berkeley. The red supergiant was first detected by the University of Hawaii’s Institute for AstronomyPan-STARRS on Haleakala, Maui, in the summer of 2020 via the huge amount of radiation from the doomed giant. And after a few months later, the supernova flared in the sky.
“It’s like watching a ticking time bomb,” says Raffaella Margutti, an adjunct associate professor at CIERA, and the paper’s senior author. “We’ve never confirmed such violent activity in a dying red supergiant star where we see it produce such a luminous emission, then collapse and combust, until now.”
The team got the chance to capture the powerful flare by obtaining the very first spectrum of the explosion, dubbed supernova 2020tlf (SN 2020tlf). The observation was done with the aid of the W.M. Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS) on Maunakea, Hawaii. Data analysis provided evidence of such dense circumstellar material around the star at the time of the explosion. This was probably the same cloud of gas that was detected around the red supergiant earlier in the summer.
From the data obtained from Keck Observatory’s Deep Imaging and Multi-Object Spectrograph (DEIMOS) and Near Infrared Echellette Spectrograph (NIRES), the team determined that SN 2020tlf was located in the NGC 5731 galaxy, some 120 million lightyears away from Earth — ten times more massive than the sun.
Super Boom Goes The Nova?
The remote access of Keck Observatory’s telescopes was integral to their research. Astronomers can connect with an on-site telescope operator in Hawaii all the way from the Evanston campus of Northwestern, where they can choose where to position the telescope. With this, they often bypass long-distance commutes to and from Hawaii. This saves astronomers precious observing time for witnessing transient events like supernovae — these easy-to-miss spectacles — and in this case, they got a glimpse at such an event.
“This significant discovery of a red supergiant supernova is yet one more strong indication of the importance of Northwestern’s investment in access to top private telescope facilities, including the Keck Observatory,” says Vicky Kalogera, a professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences, and director at CIERA.
“The Keck telescopes,” he added, “currently the best on our planet, uniquely enable scientific advances of this caliber as CIERA researchers have shown since our Keck partnership started just a few years ago.”
“I am most excited by all of the new ‘unknowns’ that have been unlocked by this discovery,” says Jacobson-Galán. “Detecting more events like SN 2020tlf will dramatically impact how we define the final months of stellar evolution, uniting observers and theorists in the quest to solve the mystery on how massive stars spend the final moments of their lives.”
Source: The Astrophysical Journal
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Written by: Nana Kwadwo, Tue, Mar 22, 2022.