A supernova is what happens to a massive star at the end of its life. Such cataclysmic explosions are known to send shock waves of compressed gas clouds far into the cosmos that eventually birth new stars. However, predicting when massive stars will reach that final violent stage has so far been beyond scientists.
Until now, perhaps. Astronomers using two telescopes in Hawaiʻi were recently able to watch a supernova unfold recently in real-time. How? They detected something nobody else had seen before—a red supergiant star noticeably brighten many months before eventually going supernova. That stage in the evolution of such stars is new to science.
Published today in The Astrophysical Journal are the results of the Young Supernova Experiment (YSE) transient survey that observed a red supergiant called SN 2020tlf during its last 130 days.
Here’s what its final, deadly detonation and transformation into a Type II supernova looked like (artist’s rendition):
“For the first time, we watched a red supergiant star explode!” said Wynn Jacobson-Galán, an NSF Graduate Research Fellow at UC Berkeley and lead author of the study. “This is a breakthrough in our understanding of what massive stars do moments before they die.”
It’s the first direct detection of a red supergiant star’s “dying breath”—a pre-explosion brightening—before an ordinary (Type II) supernova.
It suggests that some red supergiant stars’ internal structure changes as they inch towards eject a torrent of gas and collapsing into a supernova.
In the summer of 2020 the Pan-STARRS telescope detected—as bright radiation—material being violently ejected from the red supergiant star that would become SN 2020tlf.
With plenty of warning the team was able to watch the star’s final demise and then capture the huge flash as it did indeed go supernova. However, it’s the witnessing of the process of a massive star transitioning into a supernova explosion that was the rarity.
“It’s like watching a ticking time bomb,” said senior author Raffaella Margutti, an associate professor of astronomy at UC Berkeley. “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.”
Follow-up observations of SN 2020tlf indicated that the red supergiant star that caused it was about 10 times more massive than the Sun.
The plan is to hunt again for luminous radiation coming from red supergiants and help solve the mystery of what massive stars do in their final moments—and the all-sky survey camera at the Vera Rubin Observatory, due for first light later this year, should help with that.
Wishing you clear skies and wide eyes.