Researchers work to unlock secrets of supernovae, exploding stars : Maui Now

Using multiple telescopes, researchers from the Weizmann Institute of Science are working to understand supernovae, exploding stars, dating back millions of light-years and considered the building blocks of the universe and life itself.

The puzzling question is: What causes stars to explode?

Scientists at the W. M. Keck Observatory on Mauna Kea, Hawaiʻi Island, are among teams of researchers gathering data from a once-in-a-lifetime supernova called SN 2023ixf, a red supergiant supernova located in the Pinwheel Galaxy. Their findings are published in Wednesday’s edition of the journal Nature.

Until recently, supernovae were considered rare. They were observed in the Milky Way, perhaps once a century. The celestial event lights up the night sky with the intensity of 100 million suns. The last observable explosion in Earth’s galaxy took place hundreds of years ago, according to an announcement from the Keck Observatory.

Advances in telescope technology have located supernovae in distant galaxies, supplying more data than previously possible. Because supernovae can’t be predicted, “astrophysicists are like space archaeologists, usually arriving at the scene after the event and trying to piece together information from the remains,” the Keck announcement says.

“That’s what makes this particular supernova different,” said doctorate student Erez Zimmerman of Professor Avishay Gal-Yam’s group at Weizmann. “We were able — for the very first time — to closely follow a supernova while its light was emerging from the circumstellar material in which the exploding star was embedded.”

The discovery was equivalent to getting to the scene of the crime while it’s ongoing.

The scientists admit they were lucky. Gal-Yam’s team applied for research time on NASA’s Hubble Space Telescope, hoping to gather ultraviolet spectral data on any supernova interacting with its environment. Instead, they got the chance to witness in real-time one of the closest supernovae in decades: a red supergiant exploding in a neighboring galaxy called Messier 101, also known as the Pinwheel Galaxy.

Koichi Itagaki, an amateur astronomer from Japan, discovered SN 2023ixf and reported it on a Friday night, March 22, which was in the middle of the weekend in Israel (the work week in Israel is Sunday-Thursday) and right before the weekend in Baltimore’s Space Telescope Science Institute – the operations center for the Hubble Telescope.

Complicating things even further, it took place two days before Zimmerman’s wedding. Nevertheless, his team quickly conducted follow-up observations of the supernova, pulling an all-nighter on March 22, and delivering the necessary measurements to NASA.

“It’s very rare, as a scientist, that you have to act so swiftly,” Gal-Yam said. “Most scientific projects don’t happen in the middle of the night, but the opportunity arose, and we had no choice but to respond accordingly.”

Not only did they succeed in getting Hubble to assume the right coordinates and angle for recording the necessary data, but because of the explosion’s relative proximity, it turned out Hubble had already made recordings in this sector of the universe many times before.

Turning to the NASA archives, Gal-Yam’s team and many other groups were able to acquire data from before the star’s eventual demise – when it was still a red supergiant in its final stages of life. This created the most complete portrait of a supernova ever: a composite of its last days and death.

Observations of SN 2023ixf consisted of UV and X-ray data from NASA’s Hubble and Swift satellites, as well as many of the best telescopes across the globe.

This included spectra captured using three of Keck Observatory’s instruments – the Keck Cosmic Web Imager, Deep Imaging and Multi-Object Spectrograph and Low Resolution Imaging Spectrometer. Each instrument provided a unique view of the supernova and how it changed over time.

The compilation of high-quality, space- and ground-based data enabled the researchers to map out the two outer layers of the exploding star and come up with a hypothesis.

“Calculations of the circumstellar material emitted in the explosion, as well as this material’s density and mass before and after the supernova, create a discrepancy, which makes it very likely that the missing mass ended up in a black hole that was formed in the aftermath of the explosion – something that’s usually very hard to determine,” said doctorate student Ido Irani of Gal-Yam’s team.

“Stars behave very erratically in their senior years,” Gal-Yam said. “They become unstable and we usually cannot be sure which complex processes occur within them because we always start the forensic process after the fact, when much of the data has already been lost.”

“This study presents a unique opportunity to better understand the mechanisms that lead to the conclusion of a star’s life and the eventual formation of something entirely new,” Zimmerman said.

Scientists may never find out what will happen to the matter that made up Messier 101’s former red supergiant, the Keck announcement said. However, the later stages of the supernova are ongoing and new data are still coming in. That means this study, along with follow-up examinations of SN 2023ixf, could provide more insight into such explosive events.