Scientists observe a red supergiant going supernova for the first time

Despite the sheer number of stars in the sky, seeing one in the throes of a supernova is still an incredibly rare occurrence. Now, for the first time, astronomers have captured a red supergiant before, during and after a supernova explosion, gathering crucial new information about these dramatic events.

“This is a breakthrough in our understanding of what massive stars do just before they die,” said lead author Wynn Jacobson-Gal├ín (UC Berkeley). “Direct detection of pre-supernova activity in a red supergiant has never been seen before in an ordinary Type II supernova. For the first time, we have seen a red supergiant explode!”

Using the Pan-STARRS telescope in Maui, Hawaii, scientists discovered the doomed red supergiant in the summer of 2020 thanks to the sheer amount of light it emitted. Later in the fall, when it went supernova, the team captured the powerful flash using the Hawaii-based Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS). They also captured the very first spectrum of the supernova, known as SN 2020tlf.

The observations showed that the star probably ejected massive amounts of compact circumstellar material just before the explosion. Previous observations showed that red giants were relatively calm before going supernova, so the new data suggests some may change their internal structure significantly before exploding. That could then result in tumultuous gas ejections just before collapse.

SN 2020tlf is located in the NGC 5731 galaxy about 120 million light-years from Earth and was about 10 times more massive than the Sun. Stars go supernova when they run out of fuel and collapse under their own gravity, causing a massive carbon fusion explosion. For that to happen, they must be large enough (8 to 15 solar masses) or they will simply collapse into a white dwarf star like our sun eventually will. Bigger than that and they could collapse into a black hole.

The discovery now allows scientists to examine red supergiant stars in search of similar types of light radiation that could signal a new supernova. “Detecting more events like SN 2020tlf will dramatically impact how we define the final months of stellar evolution…in the quest to solve the mystery of how massive stars spend the final moments of their lives,” he said. Jacobson-Galan.

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