The explosive death of a star – a supernova – is one of the most violent astronomical events, but exactly what this phenomenon looks like as it unfolds remains a mystery.
Scientists have observed for the first time the very early stages of a supernova, with a massive star exploding into a characteristic olive shape.
The researchers used the European Southern Observatory's Very Large Telescope (VLT) based in Chile to observe the supernova, which involved a star about 15 times the mass of our own star, our sun, located in a galaxy called NGC 3621, about 22 million light-years from Earth in the direction of the constellation Hydra.
Note that a light year is the distance light travels in one year (9.5 trillion kilometers).
The shape of such eruptions has been difficult to determine until now because of the speed with which they occur. The explosion was spotted on April 10, 2024, around the time astrophysicist Yi Yang of Tsinghua University in China arrived in San Francisco with a formal request a few hours later to turn the VLT toward the supernova, which was granted.
Thus, the researchers were able to observe the explosion just 26 hours after the initial detection and 29 hours after material from the interior of the star first crossed the stellar surface. What they saw was the doomed star surrounded at its equator by a pre-existing disk of gas and dust, with the explosion pushing material outward from the stellar core, distorting the star's shape into something resembling an olive.
The explosion did not blow the star into a spherical shape. Instead, the explosion pushed violently outwards on opposite sides of the star.
"Data from a supernova explosion provides fundamental information about stellar evolution and the physical processes that lead to these celestial fireworks," said Yang, lead author of the study published in the journal Science Advances.
He also noted that "the exact mechanisms behind the supernova explosions of massive stars, those with masses over eight times the mass of the sun, are still being debated and are one of the fundamental questions scientists want to answer."
He added that the VLT's first observations captured the phase when matter accelerated by the explosion near the star's center crossed the star's surface, the photosphere.
Once the impact shock, he continued, penetrates the surface, it releases enormous amounts of energy. The supernova then brightens and becomes observable. During a brief phase, the initial shape of the supernova explosion can be studied before the explosion interacts with the material surrounding the dying star, Yang said.
This shape, he noted, offers clues as to how the explosion in the star's heart was triggered.
The new observations appear to rule out some current scientific models of the explosion process, Yang said, as scientists improve their understanding of the deaths of massive stars.
