Red supergiant stars are quiet and peaceful before exploding into a Type II supernova — but not this one. Observation is important because it suggests that some supergiant stars experience significant internal changes before they become supernovae
The Type II supernova was discovered on September 16, 2020, but astronomers have already monitored significant activity before the explosion during the previous 130 days. At the WM Keck Observatory Media Release, Raffaella Margutti, an associate professor of astronomy at the University of California, Berkeley, said it was “like watching a time bomb.”
Type II supernovae are the result of a sudden collapse and violent explosion of massive stars. Only stars between eight and about 40 stellar masses go through this form of death. “We’ve never confirmed such violent activity in a dying red supergiant star where we see it producing such a dazzling emission, then collapse and burning, so far,” said Margutti, senior author of the new study, published in the Astronomical Journal.
Indeed, rare observations shed new light on the conditions and processes involved in type II supernovae. “This is an advance in our understanding of what massive stars do moments before they die,” said Wynn Jacobson-Galán, lead author of the study and astronomer at the University of California, Berkeley. “Direct detection of pre-supernova activity in a red supergiant star has never been observed before in a common type II supernova.”
The explosion, designated SN 2020tlf, was detected by the Young Supernova Experiment transient research, the purpose of which is to “find statistical samples of young, red and rare transient phenomena.” [i.e. short-lived celestial events], better understand the variability of the black hole and limit the fundamental cosmological parameters of the universe. ”
The team used the Pan-STARRS telescope and the WM Keck Observatory, both in Hawaii, to observe the red supergiant and supernovae afterwards. Pan-STARRS, for a period of approximately 130 days, monitored huge amounts of radiation emanating from the red supergiant, while Keck, with its low-resolution recording spectrometer, monitored the supernova’s first flash, initial spectra and behavior after the supernova.
SN 2020tlf is located 120 million light years from us in the galaxy NGC 5731. The doomed star, estimated at 10 to 12 solar masses, was surrounded by dense stellar material before and during the explosion, according to a new study.
A new observation suggests that some supergiant stars experienced violent eruptions and bright explosions in the months and weeks before they became supernovae. Previous observations have suggested a period of lull before the storm, but not all supergiant stars experience the same way, new data show.
Detection of “precursor emission”, as described in the paper, combined with the presence of thick stellar material, suggests that some kind of physical mechanism is responsible for the observed loss of mass and luster. At the same time, the bright radiation produced by the red supergiant during its last months “suggests that at least some of these stars must undergo significant changes in their internal structure that then result in violent gas emissions in moments before they collapse,” the press release said.
Looking ahead, researchers with the Young Supernova experiment will now look for other examples of bright radiation coming from red superdons, and will then link this behavior to impending supernova explosions.
“I am most excited about all the new‘ unknowns ’unlocked by this discovery,” Jacobson-Galán said. “Discovering more events like SN 2020tlf will dramatically affect how we define the final months of stellar evolution, uniting observers and theorists looking to solve the mystery of how massive stars spend the last moments of their lives.”