Astronomy: Initial geometry of a supernova explored for the first time
When a star explodes, it expands at high speed. What a supernova looks like immediately after its onset was therefore unknown – until now.
Artistic representation of the determined geometry of the initial explosion
(Image: ESO/L. Calçada)
Last spring, the Very Large Telescope (VLT) succeeded for the first time in observing the explosion of a massive star almost immediately after its onset and in determining the geometry of the ejected material. The European Southern Observatory (ESO) has now made this public and released an artistic representation of this earliest possible phase of such a stellar explosion. If the observatory had been directed at the event just one day later, it would no longer have been observable. The responsible parties explain the significance of the discovery. The VLT observed the explosion, which occurred 22 million light-years away, just 26 hours after its original discovery, thanks to the rapid reaction of the study leader.
Rapid reaction as the basis for success
(Image:Â ESO/Y. Yang et al.)
As the research institution recalls, a precise balance exists throughout the life of a typical star between the force of gravity pulling it together and the opposing pressure from “its nuclear engine.” If the energy source is depleted, the star's core collapses, the surrounding mass falls onto it and is ejected. The resulting shock wave then destroys the star from within, creating a supernova. However, the breakthrough of this shock wave through the star's surface can only be observed for a few hours; afterward, the expanding explosion interacts with material around the star. It is precisely this narrow time window that has now been used for detailed observations with the VLT for the first time.
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The success was therefore due to the rapid reaction of astronomer Yi Yang from Tsinghua University in Beijing. When the supernova designated SN 2024ggi was discovered on April 10, 2024, he had just landed in San Francisco after a long-haul flight. Twelve hours later, his application for an observation with the VLT was submitted to ESO, which was immediately granted. On April 11, it was directed at the explosion, which is why the geometry of the supernova could be determined. The FORS2 instrument was decisive for this, with its data revealing that the ejected material had the shape of an olive. The axis of symmetry remained unchanged during the explosion, even as the shape flattened.
The research team was able to infer the geometry from the polarization of the light captured by the telescope. The observation changes our understanding of stellar explosions, explains co-author Ferdinando Patat from ESO. Thanks to the knowledge gained, some supernova models can already be ruled out and others improved, he adds. The team identified a red supergiant with about 12 to 15 solar masses as the precursor to the explosion, with a radius about 500 times larger than that of the Sun. The work will be presented in a scientific paper, which will be published in the scientific journal Science Advances.
(mho)
