Astronomers Watch a Star Die and Then Explode as a Supernova – For the Very First Time

img_0.5783292061641279.jpg

For the first time, a team of astronomers have imaged in real-time as a red supergiant star reached the end of its life. They watched as the star convulsed in its death throes before finally exploding as a supernova.

And their observations contradict previous thinking into how red supergiants behave before they blow up.

A team of astronomers watched the drama unfold through the eyes of two observatories in Hawaii: Pan-STARRS on Haleakala, Maui, and the W. M. Keck Observatory on Maunakea, Hawaii Island. Their observations were part of the Young Supernova Experiment (YSE) transient survey. They watched the supernova explosion, named SN 2020tlf, during the final 130 days leading up to its detonation.The team used the Keck Observatory’s Low-Resolution Imaging Spectrometer (LRIS) to capture the supernova’s first spectrum. The LRIS data showed circumstellar material around the star when it exploded. That material is likely what Pan-STARRS saw the star ejecting in the summer before it exploded.

“Keck was instrumental in providing direct evidence of a massive star transitioning into a supernova explosion,” said senior author Raffaella Margutti, an associate professor of astronomy at UC Berkeley. “It’s like watching a ticking time bomb. We’ve never confirmed such violent activity in a dying red supergiant star where we see it produce such a luminous emission, then collapse and combust, until now.”After the explosion, the team turned to other Keck instruments to continue their observations. Data from the DEep Imaging and Multi-Object Spectrograph (DEIMOS) and Near Infrared Echellette Spectrograph (NIRES) showed that the progenitor star was 10 times more massive than the Sun. The star is in the NGC 5731 galaxy about 120 million light-years away.

The team’s observations led to some new insight into Type II supernovae and their progenitor stars. Prior to these observations, nobody had seen a red supergiant display such a spike in luminosity and undergo such powerful eruptions before exploding. They were much more placid in their final days as if they accepted their fates.
Red supergiant stars eject material prior to core collapse. But that material ejection takes place on much longer timescales than SN 2020tlf. This supernova emitted circumstellar material (CSM) for 130 days prior to collapse, and that makes it a bit of a puzzle. The bright flash prior to the star’s explosion is somehow related to the ejected CSM, but the team of researchers isn’t certain how they all interacted.

img_0.42483222922823616.jpg