Thanks to the swift observations made using the Very Large Telescope (VLT) from the European Southern Observatory, scientists have unveiled the fiery end of a star right as its explosion was breaking through the surface. This exceptional moment marks the first time researchers were able to see the blast’s early shape as it was happening.
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This fleeting initial phase wouldn’t have been capturable a day later, resolving multiple queries about supernovae and their evolution.
When the supernova d SN 2024ggi was first spotted on the evening of April 10, 2024, Yi Yang, who is an assistant professor at Tsinghua University in Beijing and the lead researcher for this study, had just arrived in San Francisco after a long journey. Realizing the need for immediate action, he jumped into action.
Within a mere 12 hours, he submitted a proposal for observations to ESO, which swiftly approved it. The VLT aimed its powerful lens at the supernova on April 11, just 26 hours after it was originally found.
Taking Advantage of a Rare Cosmic Event
Located in the NGC 3621 galaxy and directed towards the Hydra constellation, SN 2024ggi lies a relatively close 22 million light-years away. With the right instruments on their telescope, the international research team knew they had a rare opportunity to explore the structure of the explosion shortly after it occurred.
“The first images from the VLT illustrated how material propelled by the star’s exploding core broke through the surface. For a limited time, we could see both the star and the explosion’s geometry at the same time,” mentioned Dietrich Baade, an ESO astronomer in Germany and co-author of the study that appeared in Science Advances.
He further stated, “Understanding the geometry of a supernova explosion is key to insights on stellar mechanics and the physical processes behind these heavenly spectacles,” Yang commented.
Diving Deeper into Supernova Mechanics
The exact processes causing supernovae in massive stars, those exceeding eight solar masses, are still up for debate and are among the core mysteries that scientists are eager to solve. The supernova’s ancestor was a red supergiant weighing between 12 and 15 solar masses and boasting a radius 500 times larger, which makes SN 2024ggi a textbook example of these enormous star explosions.
As we understand, during their lifecycle, stars maintain a spherical form due to a balance between the gravitational forces that try to compress them and the expansive power of their nuclear reactions. When a star runs out of fuel, its nuclear energy production begins to falter.
For massive stars, this loss of fuel signals the onset of a supernova: the dying star’s core collapses, the surrounding masses crash down, then bounce off. This bounce triggers a wave of shock that propels outward, ripping the star apart.
Once this shockwave reaches the surface, it releases an immense energy spike—what we see as a supernova that exponentially brightens and becomes observable. During this brief initial breakout period, we can study the earliest shape of the explosion before it interacts with the surrounding materials.
Unfolding the Explosion’s Hidden Structure
This ground-breaking achievement by astronomers, using chronometric techniques known as ‘spectropolarimetry,’ provides insights into the explosion’s geometry that other forms of observation can’t offer—primarily due to the very small angular scales involved. Lifan Wang, a co-author and professor at Texas A&M University who began his career at ESO, highlighted that.
Even though the star appears just as a single dot of light, the polarization of its emitted light holds significant clues to its structure which the researchers successfully decoded.
The only facility in the Southern Hemisphere capable of this nuanced measurement is the FORS2 instrument at the VLT. From the data gathered, astronomers discovered that the initial explosion resembled the shape of an olive.
As the explosion spread and interacted with nearby matter, the shape flattened; nonetheless, the symmetry along its axis remained constant.
What This All Means for Supernova Research
“The findings point to a consistent physical mechanism driving the explosion of various massive stars, characterized by a distinct axial symmetry,” Yang asserted.
This understanding will allow astronomers to disregard some existing supernova models and integrate valuable data to refine others, granting them greater insights into the powerful deaths of massive stars.
“This momentous discovery not only refines our comprehension of cosmic explosions but also highlights what can be accomplished when science exceeds borders,” said Ferdinando Patat, another ESO researcher and co-author.
“It’s a potent reminder that curiosity, collaboration, and prompt responses can unveil critical understandings about the universe’s mechanics.”
For further details: Yi Yang et al, An axisymmetric shock breakout indicated by prompt polarized emission from the Type II supernova 2024ggi, Science Advances (2025). DOI: 10.1126/sciadv.adx2925.www.science.org/doi/10.1126/sciadv.adx2925
Provided by ESO
This story first appeared on Phys.org.
