Free Astronomy Magazine January-February 2022

49 ASTRO PUBLISHING understand what was happening to the star just before it died. “We rarely get to examine this very close-in circumstellar material since it is only visible for a very short time, and we usually don’t start observ- ing a supernova until at least a few days after the explosion,” explained Samaporn Tinyanont, lead author on the study’s paper published in the Monthly Notices of the Royal Astronomical Society . “For this su- pernova, we were able to make ultra-rapid observations with Hub- ble, giving unprecedented coverage of the region right next to the star that exploded.” The team looked at Hubble obser- vations of the star going back to the 1990s. TESS provided an image of the system every 30 minutes start- ing several days before the explo- sion, through the explosion itself, and continuing for several weeks. Hubble was used again starting only hours after astronomers first detected the explosion. And from studying the circumstellar material with Hubble, the scientists gained an understanding of what was hap- pening around the star in the previ- ous decade. By combining all of this information, the team was able to create a multi-decade look at the star’s final years. “Now we have this whole story about what’s happening to the star in the years before it died, through the time of death, and then the af- termath of that,” said Foley. “This is really the most detailed view of stars like this in their last moments and how they explode.” Tinyanont and Foley called SN 2020fqv “the Rosetta Stone of su- pernovas.” The ancient Rosetta Stone, which has the same text in- scribed in three different scripts, helped experts learn to read Egypt- ian hieroglyphs. In the case of this supernova, the science team used three different methods to determine the mass of the exploding star. These included comparing the properties and the evolution of the supernova with theoretical models; using informa- tion from a 1997 archival Hubble image of the star to rule out higher- mass stars; and using observations to directly measure the amount of oxygen in the supernova, which probes the mass of the star. The re- sults are all consistent: around 14 to 15 times the mass of the Sun. Accu- rately determining the mass of the star that explodes in a supernova is crucial to understanding how mas- sive stars live and die. “People use the term ‘Rosetta Stone’ a lot. But this is the first time we’ve been able to verify the mass with these three different methods for one supernova, and all of them are consistent,” said Tinyanont. “Now we can push forward using these different methods and com- bining them, because there are a lot of other supernovas where we have masses from one method but not another.” In the years before stars explode, they tend to become more active. Some astronomers point to the red supergiant Betelgeuse, which has recently been belching significant amounts of material, and they won- der if this star will soon go super- nova. While Foley doubts Betel- geuse will imminently explode, he does think we should take such stel- lar outbursts seriously. “This could be a warning system,” said Foley. “So if you see a star start to shake around a bit, start acting up, then maybe we should pay more attention and really try to un- derstand what’s going on there be- fore it explodes. As we find more and more of these supernovas with this sort of excellent data set, we’ll be able to understand better what’s happening in the last few years of a star’s life.” NASA satellite designed primarily to discover exoplanets, with the ability to detect an assortment of other phenomena. They quickly trained Hubble and a suite of ground-based telescopes on it. Together, these observatories gave the first holistic view of a star in the very earliest stage of destruction. Hubble probed the material very close to the star, called circumstellar material, mere hours after the ex- plosion. This material was blown off the star in the last year of its life. These ob- servations allowed astronomers to !