The initial detection of SN 2024ggi occurred on the night of April 10, 2024, local time. Yang, just arriving in San Francisco from Beijing, learned of the supernova and immediately began the process to secure rapid VLT observations. Within twelve hours, an observing proposal was submitted to ESO, and approval followed swiftly. The VLT targeted the event a mere 26 hours after detection, an interval critical for observing the blast while it was still emerging from the star's surface.
The research team took advantage of the early phase, when the geometry of the explosion and progenitor could be directly studied. Dietrich Baade, an ESO astronomer and study co-author, stated, "The first VLT observations captured the phase during which matter accelerated by the explosion near the centre of the star shot through the star's surface. For a few hours, the geometry of the star and its explosion could be, and were, observed together."
Supernova geometry offers clues to the processes shaping stellar evolution and death, particularly for red supergiant stars many times more massive than the Sun. The progenitor behind SN 2024ggi was estimated to be 12 to 15 solar masses, with an expanded radius 500 times that of the Sun. These massive stars maintain equilibrium through a balance of gravity compressing inward and nuclear fusion creating outward pressure. Collapse begins when fusion ceases, causing the stellar core to condense under its own gravity. Shells of overlying mass crash inward, rebound, and send out a shockwave that ultimately rips apart the star.
A supernova becomes visible when this shock finally pierces the surface, emitting tremendous energy. This "breakout" phase lasts only a few hours before debris expansion and interaction with surrounding matter distort the original shape. By reaching SN 2024ggi so soon after the blast, the team could document this brief window before critical details faded.
To discern the explosion's structure, the VLT's FORS2 instrument was used for spectropolarimetry, a technique that measures how light polarization reveals geometry otherwise invisible at such distances. Lifan Wang, professor at Texas A and M University and co-author, remarked, "Spectropolarimetry delivers information about the geometry of the explosion that other types of observation cannot provide because the angular scales are too tiny." Even though SN 2024ggi appeared as a single point of light, polarimetric signatures exposed the true shape of the blast.
The data revealed the initial ejection resembled an olive, rather than a perfect sphere. As the expanding material encountered external gas and dust, its profile flattened out but maintained a single symmetry axis - evidence for a consistent physical mechanism in massive-star explosions. "These findings suggest a common physical mechanism that drives the explosion of many massive stars, which manifests a well-defined axial symmetry and acts on large scales," Yang explained.
This observation gives astronomers the data needed to challenge or refine prevailing models of supernova formation. Some hypothetical mechanisms can now be excluded, while others may see their credence strengthened. Co-author Ferdinando Patat added, "This discovery not only reshapes our understanding of stellar explosions, but also demonstrates what can be achieved when science transcends borders. It's a powerful reminder that curiosity, collaboration, and swift action can unlock profound insights into the physics shaping our Universe."
Research Report:An axisymmetric shock breakout indicated by prompt polarized emission from the type II supernova 2024ggi
Related Links
ESO (European Southern Observatory)
Stellar Chemistry, The Universe And All Within It
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
