By Will Dunham
WASHINGTON (Reuters) -The explosive death of a star – a supernova – is among the most violent cosmic events, but precisely how this cataclysm looks as it unfolds has remained mysterious. Scientists now have observed for the first time the very early stages of a supernova, with a massive star exploding in a distinctive olive-like shape.
The researchers used the European Southern Observatory’s Chile-based Very Large Telescope, or VLT, to observe the supernova, which involved a star roughly 15 times the mass of our sun residing in a galaxy called NGC 3621 about 22 million light-years from Earth in the direction of the constellation Hydra. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
The shape of such explosions has been hard to nail down until now because of how rapidly they take place, so it took quick action with this supernova. The explosion was detected on April 10, 2024, around the time astrophysicist Yi Yang of Tsinghua University in China had landed on a long flight to San Francisco. Yang’s formal request just hours later to aim the VLT at the supernova was granted.
The researchers thus were able to observe the explosion just 26 hours after the initial detection and 29 hours after material from inside the star first broke through the stellar surface.
What they saw was the doomed star surrounded at its equator by a preexisting disk of gas and dust, with the explosion pushing material outward from the stellar core to distort the star’s shape into one resembling a vertical-standing olive. The explosion notably did not blow the star apart in a spherical shape. Instead, the explosion pushed violently outward at opposite sides of the star.
“The geometry of a supernova explosion provides fundamental information on stellar evolution and the physical processes leading to these cosmic fireworks,” said Yang, lead author of the study published on Wednesday in the journal Science Advances.
“The exact mechanisms behind supernova explosions of massive stars, those with more than eight times the mass of the sun, are still debated and are one of the fundamental questions scientists want to address,” Yang said.
Big stars like those live relatively short lives. This one, a type called a red supergiant, was about 25 million years old at the time of its demise. In comparison, the sun is more than 4.5 billion years old and has a few more billion years to go.
At the time it exploded, this star’s diameter was 600 times greater than the sun. Some of the star’s mass was blown into space in the explosion. The remainder is believed to have become a neutron star, a highly compact stellar remnant, according to study co-author Dietrich Baade, a Germany-based astrophysicist at the European Southern Observatory.
When a star exhausts the hydrogen fuel for the nuclear fusion occurring at its center, its core collapses, which then sends material blasting outward, penetrating the stellar surface and into space.
“The first VLT observations captured the phase during which matter accelerated by the explosion near the center of the star shot through the star’s surface, the photosphere,” Yang said.
“Once the shock breaks through the surface, it unleashes immense amounts of energy. The supernova then brightens dramatically and becomes observable. During a short-lived phase, the supernova’s initial ‘breakout’ shape can be studied before the explosion interacts with the material surrounding the dying star,” Yang said.
This shape, Yang said, offers clues about how the explosion was triggered at the heart of the star. The new observations seem to rule out some current scientific models of the explosion process, Yang said, as scientists refine their understanding of the deaths of massive stars.
(Reporting by Will Dunham; Editing by Daniel Wallis)
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