Despite the large number of stars in the sky, detecting one in the midst of a supernova is still an incredibly rare event. Now astronomers captured a red supergiant before, during and after a supernova explosion for the first time, gathering crucial new information about these dramatic events.
“This is a breakthrough in our understanding of what massive stars do moments before they die,” said lead author Wynn Jacobson-Galán (UC Berkeley). “Direct detection of pre-supernova activity in a red supergiant star has never been observed before in a common Type II supernova. For the first time, we saw a red supergiant star explode!”
Using the Pan-STARRS telescope in Maui, Hawaii, scientists detected the doomed red supergiant star in the summer of 2020, thanks to the massive amount of light it was emitting. Later in the fall, when it turned into a supernova, the team captured the powerful flash using the Low Resolution Imaging Spectrometer (LRIS) from Hawaii-based Keck Observatory. They also captured the first supernova spectrum, known as SN 2020tlf.
Observations showed that the star likely ejected large amounts of dense circumstellar material just before the explosion. Previous observations have shown that red giants were relatively calm before becoming supernovae, so the new data suggests that some may significantly change their internal structure before exploding. This could result in tumultuous gas ejections moments before the collapse.
SN 2020tlf is located in galaxy NGC 5731 about 120 million light years from Earth and was about 10 times more massive than the Sun. Stars turn into supernovae when they run out of fuel and collapse into their own gravity, feeding them a huge explosion of carbon fusion. For this to happen, they must be large enough (8 to 15 solar masses) or they will simply collapse into a white dwarf star, as our Sun eventually will. Anything bigger than that and they could fall apart into a black hole.
The discovery will now allow scientists to search red supergiant stars for similar types of light radiation that could signal another supernova. “Detecting more events like SN 2020tlf will dramatically affect how we define the final months of stellar evolution … in an attempt to solve the mystery of how massive stars spend the final moments of their lives,” said Jacobson-Galán.
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