The last days of a star before its supernova explosion

In the famous series ” Once upon a time in space »By Albert Barillé, Humanity of the XXXI^e century has the chance to witness the transformations of a star unstable just before it explodes in supernova for the first time in its history, an event which, in addition, does not occur statistically in the Milky Way only once a century or so.

Reality has partly caught up with fiction already in the 21st century^e century, as an article published in The Astrophysical Journal, free access deposited on arXiv, and coming from a team ofastronomers conducted by researchers at Northwestern University and the University of California at Berkeley (UC Berkeley).

It all started in the summer of 2020 with the detection of a particularly bright star using Pan-Starrs (acronym of Panoramic Survey Telescope And Rapid Response System, ” Telescope panoramic survey and rapid response system ”), an astronomical survey program whose objective is to perform astrometry and photometry for transient events over a large part of the sky, almost continuously with a telescope located at the top of Haleakalā, Hawaii.

A red supergiant of 10 solar masses

The study of the star showed that it contained 10 solar masses and that it was located in the galaxy NGC 5731 about 120 million light years from the Milky Way. In phase of supergiant red, so she was monitored for 130 days as part of the Young Supernova Experiment (YSE) conducted with Pan-Starrs. The star eventually became a type supernova SN II at the end of this period and it was then observed also with the instruments of the WM Keck Observatory on the Maunakea, also in Hawaii.

The significance of the discovery can be read through the statements of Wynn Jacobson-Galán, NSF graduate researcher at UC Berkeley and lead author of the article in The Astrophysical Journal : ” This is a breakthrough in our understanding of what massive stars do moments before they die. Direct detection of pre-supernova activity in a supergiant star red has never been seen before in an ordinary Type II supernova. For the first time we saw a red supergiant star explode ! “

According to the press release from WM Keck Observatory Regarding the supernova which has been dubbed SN 2020tlf, the measurements taken challenge our previous ideas of how red supergiant stars evolve just before they explode. All the previous observations did not show any warning signs, that is to say of important changes in the activity of the parent stars of SN II which could lead to believe that the thermonuclear explosion was imminent. The stars were calm, without analogues of strong solar flares.

But the case of SN 2020tlf, unless we were lucky enough to actually observe its star in the final moments before the explosion, suggests that at least some massive stars must have their convective equilibrium seriously altered little. time before the star catastrophe. Indeed, the Pan-Starrs data already showed strong ejections of plasma from the parent star and shortly after the explosion the Keck also showed the presence of a dense circumstellar environment around the current explosion, confirming massive ejection of matter previously.

” Detecting more events like SN 2020tlf will have a huge impact on how we define the final months of stellar evolution, uniting observers and theorists in the quest to solve the mystery of how massive stars pass the last. moments of their life », Concludes Jacobson-Galán.

The study of SN 2020tlf joins that of another supernova studied with Hubble.