Astronomers have captured the first image of a giant dying star.
Just 26 hours after supernova SN 2024GGI was first detected in April 2024, the European Southern Observatory (ESO) pointed its Very Large Telescope (VLT) in Chile at the dramatic astronomical event. Supernovae are the explosive deaths of stars, and ESO’s VLT managed to capture it in the early moments – just as the explosion was moving across the star’s surface. This achievement reveals, for the first time, the shape of the early, short-lived phase of a supernova.
This is great news for researchers because “the geometry of supernova explosions provides fundamental information on stellar evolution and the physical processes leading to these cosmic fireworks,” Yi Yang, an astronomer at Tsinghua University and co-author of a study published today in Science Advances, explained in an ESO statement.
an explosive secret
As iconic as supernovae are, researchers continue to debate how massive stars – stars with more than eight times the mass of the Sun – become supernovae. When a massive star runs out of fuel, its core collapses and its surrounding sphere of mass collapses inward before rebounding into a rebound shock, which expands outward and releases enormous amounts of energy as it breaks through the star’s surface. Only then does the supernova become bright and observable.
Yang and his colleagues write in the study, “The death of giant stars is caused by a collapse-induced buoyancy shock that disrupts the star. How such a shock initiates and propagates through the star has been a decades-old puzzle.” Just 22 million light-years away, in the galaxy NGC 3621, supernova SN 2024GGI isn’t too far away by astronomical standards. Before the explosion, it was a red supergiant with a mass 12 to 15 times that of the Sun and a radius 500 times larger.
The team was able to capture the short-lived “breakout” shape for the first time with a technique called spectropolarimetry – before the explosion interacted with the material surrounding it. The technique “provides information about the geometry of the explosion that other types of observations cannot provide,” said study co-author Lifan Wang, an astronomer at Texas A&M University.
If you’re imagining a detailed picture of a colorful explosion, that’s not what we’re talking about here (the feature image above is an artist’s interpretation based on the new data). The supernova appears as a single point, but researchers were able to reconstruct its geometry from the polarization of its light. Simply put, polarization is a property of light particles that, in some cases, allows researchers to estimate the size of the star or supernova that is emitting the light.
olive shape
The team found that the initial explosion was olive-shaped, and as material expanded outward and collided with matter around the star, it flattened but maintained the same axis of symmetry. Yang said, “These findings suggest a common physical mechanism that drives the explosion of many giant stars, which reveals a well-defined axial symmetry and acts on larger scales.”
Thanks to these results, astronomers can now reject many existing supernova models and improve others, while respecting the precise nature of these powerful explosions.