When very large stars run out of fuel and reach the end of their lives, they can explode in massive, dramatic events called supernovas. These explosions throw off enormous amounts of light and energy, but there’s much we still don’t know about how this process happens. Now, astronomers have observed a red supergiant star going supernova for the first time, catching a glimpse of the massive star’s final moments of life.
“This is a breakthrough in our understanding of what massive stars do moments before they die,” said Wynn Jacobson-Galán, lead author of the study, in a statement. “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!”
An artist’s impression of a red supergiant star in the final year of its life emitting a tumultuous cloud of gas. This suggests at least some of these stars undergo significant internal changes before going supernova. W. M. Keck Observatory/Adam Makarenko
The team observed the supernova SN 2020tlf using two telescopes in Hawai’i, Pan-STARRS, and the W. M. Keck Observatory. They were able to spot the red supergiant before the supernova occurred as it was giving off significant amounts of light as well as ejecting large amounts of gas. They observed the star for 120 days before it went supernova in fall 2020, and they saw a dense cloud of gas surrounding the star when it exploded.
“Keck was instrumental in providing direct evidence of a massive star transitioning into a supernova explosion,” said senior author Raffaella Margutti, an associate professor of astronomy at UC Berkeley. “It’s like watching a ticking time bomb. 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 star which exploded was particularly large, at 10 times the mass of the sun, and was located 120 million light-years away in the galaxy NGC 5731. It is of particular interest to researchers as it was so active before exploding, while previously observed red supergiants have been relatively calm before going supernova.
“I am most excited by all of the new ‘unknowns’ that have been unlocked by this discovery,” said 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 of how massive stars spend the final moments of their lives.”
The results are published in The Astrophysical Journal.