Ground-based telescopes have provided the first real-time look at the pain of dying a red giant star. While these are not the brightest or most massive stars, they are by far the largest.
However, the star at the heart of this new research, located in the galaxy NGC 5731 about 120 million light-years from Earth, was 10 times the mass of the Sun before it exploded.
Before they step out in the glow of glory, some stars experience violent explosions or release glowing layers of gas. Until astronomers witnessed this event, they believed that the red giant planets were relatively quiet before exploding into a supernova or collapsing into a dense neutron star.
Instead, scientists watched the star dramatically self-destruct before collapsing into a Type II supernova. This star death is the rapid collapse and violent explosion of a massive star after it burns through hydrogen, helium, and other elements in its core.
“This is a breakthrough in our understanding of what massive stars do moments before they die,” said study lead author Wayne Jacobson Galan, a graduate research fellow at the National Science Foundation at the University of California, Berkeley, in a statement.
“Direct detection of pre-supernova activity in a red giant star has not been observed before in an ordinary type II supernova. For the first time, we watched a red giant star explode.”
The last moments of astral death
Astronomers were first alerted to the star’s unusual activity 130 days before a supernova. The bright radiation was detected in the summer of 2020 by the University of Hawaii’s Pan-STARRS Astronomy Telescope on Haleakala on Maui.
Then that fall, researchers saw a supernova in the same place.
They observed this using the Low Resolution Imaging Spectrometer of the WM Keck Observatory in Maunakea, Hawaii, and named it supernova 2020tlf. Their observations revealed the presence of matter around the star when it exploded – the bright gas that the star violently expelled away from itself during the summer.
“It’s like watching a ticking time bomb,” senior study author Raffaella Margotti, associate professor of astronomy and astrophysics at UC Berkeley, said in a statement. “We have never confirmed such violent activity in a dying red giant star that we see it produce such a luminous emission, then collapse and ignite, until now.”
The discovery showed that some of these massive stars likely undergo consequential internal changes that cause turbulent release of gas before their death.
The work was conducted while Jacobson Gallan and Margotti were still at Northwestern University. They had remote access to telescopes at the Keck Observatory in Hawaii, which was “useful in providing direct evidence of a massive star turning into a supernova explosion,” Margotti said.
“I am very excited about all the new ‘unknowns’ that have been revealed through this discovery,” Jacobson Gallan said. “The discovery of more events like SN 2020tlf will greatly 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 their last moments.”