In A First, Astronomers Capture Real-Time Death Of A Star And Subsequent Supernova Explosion

Astronomers have captured the real-time death of a red supergiant for the first time. They watched the massive star rapidly destroying itself, and the violent activities during its final moments.

An artist's impression of a red supergiant star in the final year of its life emitting a tumultuous cloud of gas. (Photo credit: W. M. Keck Observatory/Adam Makarenko)

New Delhi: Astronomers have captured the real-time death of a red supergiant for the first time. They watched the massive star rapidly destroying itself, and the violent activities during its final moments. The massive star subsequently exploded into a Type II supernova, which is a supernova occurring in larger stars of at least eight solar masses. A Type II supernova starts fusing increasingly heavy elements in shells around the core after it leaves the main sequence.  
These supernovae result from the collapse of massive stars, or the collapse of the star's iron core. Once the star starts fusing silicon, iron is created as the end product. The iron burns through fission rather than fusion, resulting in the creation of a series of layers within the star.
The discovery was recently published in The Astrophysical Journal. 

The Red Supergiant Experienced A Deadly Detonation During Its Last 130 Days

A team of researchers conducting the Young Supernova Experiment (YSE) transient survey observed the red supergiant during its last 130 days at the end of which it experienced a deadly detonation. The astronomers used two Hawaii telescopes — the University of Hawaii Institute for Astronomy Pan-STARRS on Haleakalā, Maui, and WM Keck Observatory on Maunakea, Hawaii Island.Wynn Jacobson-Galán, the lead author of the study, said this is a breakthrough in astronomers' understanding of what massive stars do moments before they die, according to a statement issued by the WM Keck Observatory. 

Scientists Observed A Massive Star Explode For The First Time

He added that direct detection of pre-supernova activity in a red supergiant star has never been observed before in an ordinary Type II supernova. He expressed his happiness over the fact that scientists, for the first time, watched a red supergiant explode.
The red supergiant was radiating a huge amount of light in the summer of 2020, which is when Pan-STARRS first detected the doomed massive star. In the fall of 2020, a supernova lit the sky. 
The astronomers quickly captured the powerful flash and obtained the very first spectrum of the energetic explosion using Keck Observatory's Low Resolution Imaging Spectrometer (LRIS). The scientists named the explosion as supernova 2020tlf, or SN 2020tlf. 
There was direct evidence of dense circumstellar material surrounding the star at the time of explosion. The scientists believe this is the same exact gas that Pan-STARRS had imaged the red supergiant violently ejecting earlier in the summer, the study said.
Senior author Raffaella Margutti said that Keck was instrumental in providing direct evidence of a massive star transitioning into a supernova explosion. Margutti added that it was like watching a ticking time bomb. 
This is the first instance in which scientists have observed a red supergiant star produce such a luminous emission, then collapse and combust.

First Instance Of A Red Supergiant Producing A Luminous Emission

Previous ideas of how red supergiant stars evolve right before blowing up were different. Earlier, all red supergiants observed before exploding showed no evidence of violent eruptions or luminous emission.
SN2020tlf is the first instance of a red supergiant producing such a luminous emission.
Based on the data obtained from Keck Observatory's DEep Imaging and Multi-Object Spectrograph (DEIMOS), and Near Infrared Echellette Spectrograph (NIRES), the scientists determined that SN 2020tlf's progenitor red supergiant star, located in the NGC 5731 galaxy around 120 million light years away from Earth, was 10 times more massive than the Sun.
The researchers noted in the study that this novel detection of bright radiation coming from a red supergiant in the final year before exploding suggests that at least some of these stars must undergo significant changes in their internal structure. This is what results in the tumultuous ejection of gas moments before they collapse.
The findings are important because it paves a path forward for transient surveys like YSE to search for luminous radiation coming from red supergiants.
Jacobson-Galán said that detecting more events like SN 2020tlf will dramatically impact how astronomers define the final months of stellar evolution, and will help observers solve the mystery on how massive stars spend the final moments of their lives.