An international team of astrophysicists has observed for the first time the earliest and most fleeting stage of a supernova explosion. This is an unusual situation that has made it possible to learn the details of the death of this type of star in a massive explosion. Thanks to a series of quick observations, very large telescope Published in the magazine this Thursday (VLT) scientific progressScientists have documented how the initial explosion was shaped like an olive and then flattened, releasing material into the void of space.
Large telescopes typically target supernovae several critical hours after their initial detection, after the explosion has shattered material and surrounded the dying star. On this occasion, the team of Yi Yang, an assistant professor at Tsinghua University in Beijing, China, reflexively called for a quick observation of that region of the sky using VLT on the night of April 10, 2024.
When the SN 2024ggi supernova explosion was detected, Yang had just landed in San Francisco after a long-distance flight and felt he needed to act quickly. Twelve hours later, ESO submitted an observation proposal to ESO, which, after a very quick approval process, pointed its VLT telescope in Chile at the supernova on April 11, just 26 hours after the initial discovery.
accelerated matter
Supernova SN 2024ggi is located just 22 million light-years away in the constellation Hydra in the galaxy NGC 3621. Equipped with large telescopes and appropriate equipment, the international team recognized a unique opportunity to determine the shape of the explosion shortly after it occurred. “The first VLT observations captured the phase in which material accelerated by an explosion near the star’s center passes through its surface,” says Dietrich Baade, an astronomer at Germany’s ESO and co-author of the study. “For several hours, we were able to observe the geometry of the star and its explosion simultaneously.”
The first VLT observations captured the phase in which material accelerated by an explosion near the star’s center passes through its surface.
dietrich bade
— Astronomer at ESO in Germany and co-author of the study.
This moment is very important because when the shock wave passes through the surface, a huge amount of energy is released. A supernova shines dramatically and no details can be observed. During the short lifetime stage, the early “fragmentation” shape of the supernova can be studied, before the explosion interacts with the material surrounding the dying star.
“The geometry of supernova explosions provides fundamental information about the evolution of stars and the physical processes that produce these cosmic spectacles,” Yang explains. The exact mechanism underlying the supernova explosion of massive stars with more than eight times the mass of the Sun is still debated and is one of the fundamental questions scientists want to solve. This supernova’s ancestor was a red supergiant star with a mass 12 to 15 times larger than the Sun and a radius 500 times larger, making SN 2024ggi a classic example of a massive star exploding.
Star’s “farewell”
We know that a typical star maintains its spherical shape throughout its life as a result of a very precise balance between the force of gravity trying to compress the star and the pressure of the nuclear engine trying to expand it. Once the last fuel source is exhausted, the nuclear engine begins to fail. For massive stars, this marks the beginning of a supernova explosion. The core of a dying star collapses, causing layers of surrounding mass to fall on top of it and bounce back. This shock wave propagates outward and causes the star to collapse.
Co-author Lifan Wang, a professor at Texas A&M University in the US, said astronomers were the first to successfully observe the early “splitting” shape of a supernova using a technique called spectropolarimetry. The technique provides information about the geometry of the explosion that other types of observations cannot provide because the angular scale is too small. Although an exploding star appears as a single point, the polarization of its light contains hidden clues about its geometry that the researchers were able to decipher.
These discoveries suggest a common physical mechanism that causes the explosion of many massive stars, which exhibits distinct axial symmetry and operates on large scales.
Iyan
— Professor at Tsinghua University in Beijing and lead author of the study
To do this, they used a FORS2 device attached to the VLT. This revealed that the initial explosion of matter was shaped like an olive. As the explosion spread outward and collided with material around the star, the shape flattened, but the axis of symmetry of the ejected material remained the same. “These discoveries suggest a common physical mechanism that causes the explosion of many massive stars, which exhibits well-defined axial symmetry and operates on a large scale,” Yang emphasizes.
With this knowledge, astronomers can rule out some of the current supernova models and add new information to improve others, gaining insight into the powerful deaths of massive stars. “This discovery not only redefines our understanding of stellar explosions, but also shows what can be achieved when science crosses borders,” says co-author Ferdinand Patat, an astronomer at ESO. “This is a powerful reminder that curiosity, collaboration, and quick action can reveal deep insights into the physics that shape our universe.”
“Great job”
Miguel Torres, an astrophysicist at the Andalucía Institute of Astrophysics (IAA), considers this a “grand and valuable study” with results that have profound implications for the physics of supernovae (type Ibc and type II), which are formed by the collapse of a nucleus. “If ESO didn’t give us time and react immediately, we wouldn’t have gotten this science,” he emphasizes.
If ESO hadn’t given it time and reacted quickly, we wouldn’t have gotten this science.
Michael Torres
— Astrophysicist at the Institute of Astrophysics of Andalusia (IAA)
For experts, these studies of polarization just hours after a supernova explosion put the final nail in the coffin of explosion models that still insisted on spherical symmetry. “A popular model seems to be one that triggers a magnetrotational process, where an amplified magnetic field carries material along the axis of rotation of the collapsing core,” Torres says.
Jonay González, a researcher at the Canary Islands Institute of Astrophysics (IAC), emphasizes the great value of being able to observe the supernova from almost the first moment until almost 200 or 300 days after its explosion. “In this case, we used a technique called spectropolarimetry to obtain information about the geometry of the explosion in three dimensions,” he points out. “Thanks to that, we can understand the direction of the explosion, and from there we can extract information about how the explosion occurs,” he points out, because the exact mechanism by which a star stops collapsing and generates an outward wavefront is still not known in detail.
By reconstructing the three-dimensional geometry of the first hours of the star’s outburst, we found that in this case it was an asymmetric outburst.
Lewis Galvany
— Astrophysicist at ICE-CSIC
ICE-CSIC astrophysicist Luis Galvani also believes we are facing an exceptional observation. “The scientific objective was to analyze the geometry of the star, which was initially spherical, just after the material had collapsed and was ejected,” he says. What was unclear was whether the explosion evolved symmetrically, maintaining the same spherical shape of the star, or, on the contrary, along a preferred axis (olive shape).
“By reconstructing the three-dimensional shape of the first hours of the star’s explosion, we found that in this case it was an asymmetric explosion,” the experts say. “This does not mean that all supernovae are like this, but it goes against the theoretical idea that all explosions are perfectly symmetric,” Galvani concludes. “This discovery transforms our understanding of how massive stars collapse and how they distribute the heavy elements that enrich the universe.”
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