Shape of Supernova: Massive star’s explosive death captured with UH astronomer’s help

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Video animation of supernova (Artist's animation shows a star going supernova. This marks the first ever observation of the shape of a supernova explosion at this very early stage. Credit: ESO/L. Calçada)

Astronomers have captured one of the universe's most dramatic moments - the instant a massive star exploded and the blast broke through the star's surface. The rare event, observed with the European Southern Observatory's Very Large Telescope, gave scientists an unprecedented look at a star's final seconds. A University of Hawaiʻi astronomer was part of the international team that raced to record and study the supernova in real time.

For the first time, researchers were able to map the three-dimensional shape of a stellar explosion as it unfolded. Their discovery, published in Science Advances, offers new clues about how giant stars live, die, and transform into supernovae that enrich the cosmos with the elements needed for life.

Chris Ashall, an assistant astronomer at the UH Mānoa Institute for Astronomy, was part of the global team that zeroed in on the stellar explosion known as SN 2024ggi. The supernova was first spotted in April 2024 in the nearby galaxy NGC 3621, 22 million light-years away in the constellation Hydra.

"As soon as the alert came in, we knew this was the kind of a relatively nearby explosion you might see once in a decade," said Ashall. "If we could move fast enough, we had a chance to watch the blast wave literally breaking out of the star's surface."

Racing to capture observations

Within hours of the discovery, the international team submitted an urgent observation request to the European Southern Observatory. Ashall helped with this effort, prompting the Very Large Telescope in Chile to target the supernova just 26 hours after it was first spotted.

​​The team used a technique called spectropolarimetry, which measures how light of different colors is polarized, to reveal the three-dimensional shape of the exploding material. They discovered that the explosion was elongated, more like an olive than a sphere. As it expanded and hit surrounding gas, the blast began to flatten but kept the same orientation, hinting that many massive stars may collapse in the same way.

The dying star was a red supergiant about 12-15 times heavier than the Sun and roughly 500 times larger. Studying its shape offers new insight into how massive stars evolve and lose mass before they die.

"This shows what's possible when you combine fast alerts, flexible telescopes, and a global team," said Ashall.

Peering deeper

Ashall's team at IfA is following the supernova with NASA's James Webb Space Telescope. Early results show clumpy debris where new molecules form, helping create one of the most detailed 3D views ever of a massive star's final moments.