Despite the huge number of stars in the sky, discovering one of them in the midst of a supernova is still an extremely rare event. Now, astronomers have captured a supernova red giant before, during and after a supernova explosion for the first time, and have gathered important 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 Wayne Jacobson Gallan (UC Berkeley). “Direct detection of pre-supernova activity in a red giant star that had not previously been observed in an ordinary type II supernova. For the first time, we saw a red giant star explode!”
Using the Pan-STARRS telescope in Maui, Hawaii, scientists discovered the doomed red giant star in the summer of 2020 thanks to the massive amount of light it emits. Later in the fall when it became a supernova, the team captured the powerful flash using the Low Resolution Imaging Spectrometer (LRIS) of the Hawaii-based Keck Observatory. They also captured the first spectrum of a supernova, known as SN 2020tlf.
Observations showed that the star likely released huge amounts of dense stellar matter prior to the explosion. Previous observations showed that the red giants were relatively quiet before the supernova occurred, so the new data suggests that some may change their internal structure dramatically before the explosion. This can then cause turbulent gases to be released moments before collapse.
SN 2020tlf is located in the galaxy NGC 5731, 120 million light-years from Earth and had a mass ten times greater than that of the Sun. Stars transform into a supernova when they run out of fuel and collapse under their own gravity, triggering a massive explosion of carbon fusion. For this to happen, it must be large enough (8 to 15 solar masses) or it will simply collapse into a white dwarf star like our Sun eventually. Anything larger than that could collapse into a black hole.
The discovery will now allow scientists to scan red giant stars for similar types of luminous radiation that could indicate another supernova. “The discovery of more events such as SN 2020tlf will greatly influence how we define the last months of stellar evolution…in the quest to solve the mystery of how massive stars spend their last moments,” said Jacobson Gallan.
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