Astronomers have for the first time detected the early shape of a star exploding, an achievement that enhances our understanding of supernova events. This groundbreaking discovery was made possible through the use of the European Southern Observatory’s (ESO) Very Large Telescope (VLT) and a technique known as “spectropolarimetry.” The team, led by Yi Yang, an assistant professor at Tsinghua University in Beijing, investigated supernova SN 2024ggi, located in the galaxy NGC 3621, approximately 22 million light-years away in the constellation Hydra.
The research team was able to gather unprecedented data on the geometry of the explosion shortly after it occurred. They observed the supernova just after its detection on the evening of April 10, 2024, with follow-up observations conducted the next day. This rapid response allowed the team to analyze the explosion’s initial shape, which had never been done before.
Revolutionizing Supernova Research
Stars typically maintain a spherical shape due to the balance between gravitational pressure and internal pressure from nuclear fusion. When a star exhausts its nuclear fuel, it experiences gravitational collapse, leading to an outward explosion of its outer layers—a supernova. During this brief phase, the initial shape of the explosion can be observed before the shock wave interacts with surrounding materials.
The innovative technique of spectropolarimetry combines spectroscopy and polarimetry to measure light polarization across various wavelengths. This method reveals details about a supernova’s explosion that are unattainable through traditional observational techniques. In most cases, the polarization of light from stars cancels out, resulting in a net polarization of zero. When astronomers detect a non-zero net polarization, they can infer the shape of the exploding star.
The only instrument capable of performing this analysis is the FOcal Reducer and low dispersion Spectrograph 2 (FORS2), which was recently installed on the VLT. This technological advancement enabled the team to uncover critical information about SN 2024ggi’s explosion.
Insights into Stellar Evolution
The progenitor star of SN 2024ggi was a red supergiant, approximately 500 times the radius of the Sun and 12 to 15 times more massive. Based on data obtained from FORS2, researchers discovered that the initial explosion had an olive-shaped geometry, which flattened as it expanded outward. Despite this change, the axis of symmetry of the ejected material remained consistent throughout the explosion.
As Dietrich Baade, an astronomer at ESO and co-author of the study, noted, “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. For a few hours, the geometry of the star and its explosion could be, and were, observed together.”
This discovery not only reshapes our understanding of how massive stars die but also highlights the effectiveness of international collaboration in advancing scientific research. The findings, published in Science Advances, allow astronomers to eliminate some existing supernova models while refining others.
The implications of this research extend beyond mere observation; they contribute to a broader understanding of stellar evolution and the mechanisms that drive supernova explosions. As scientists continue to analyze supernovae like SN 2024ggi, they move closer to answering fundamental questions about the life cycles of stars and the dynamics of the universe.
