The shape of a supernova was first observed within hours of the explosion. This was done by an international team of astronomers, who managed to capture the data on SN2024 todaysupernova exploded in the galaxy NGC3621 to 22 million light-years on April 10, 2024. The observations took place with Very Large Telescope (VLT) in Chile. Using the technique of spectropolarimetryastronomers have discovered how a supernova explosion initially possesses a axial symmetrysimilar to one olive, instead of spherical as previously thought. A supernova is the final explosive stage of stars with a mass greater than 8 solar masses capable of emitting as much energy in a few seconds as the Sun does in its entire lifeeven exceeding the brightness of an entire galaxy. The supernova in question was the result of the collapse of a star red supergiantwith a mass 12 to 15 times that of the king of the Solar System and a radius 500 times larger. The study will allow us to investigate these cosmic fireworks more deeply, allowing us to refine the models that describe their behavior.
The study of the true shape of the supernova: close observation over time
The April 10, 2024 the supernova SN2024 today exploded in the galaxy NGC3621 22 million light-years from Earth in the direction of the constellation Hydra. Thanks to the promptness of Yi Yangprofessor at Sinhua University in Beijing and lead author of the study, in Sun 26 hours away the big eyes of VLT telescope in Chile they were pointed in the direction of the supernova. Thanks to this one such close observationcombined with the technique of spectropolarimetryastronomers were able to observe the true form of a supernova explosion before it interacts with the surrounding material.
An explosion of supernova it is the final outcome of the stars life of mass greater than 8 solar masses. The latter, having synthesized iron and nickel in the nucleus, are no longer able to sustain themselves through nuclear fusion reactions, thus leaving the outer layers of the dying star free of collapse due to gravity towards the central iron and nickel core. Collapse occurs at speeds close to those of lightaccumulating more and more material in the nucleus which at a certain point will hardens (due to the formation of a neutron nucleus) causing a rebound of the material still falling towards the center. This bounce generates a shock wavethe supernova explosion that causes a disintegration of the star.
Initially it was thought that this shock wave had spherical symmetry, that is, that it propagated equally in all directions. The new study instead shows us how theshock wave propagates outwards in preferential directionswith one axial symmetrysimilar to an olive. However, this symmetry is maintained only in the initial stages of the explosion, since the interaction with the material surrounding the star changes the symmetry to a spherical-like one. Thanks to this new data, astronomers will be able to better understand the nature of these extreme events, discarding those physical models that do not provide axial symmetry and at the same time refining those that do.
How the shape of the newly exploded supernova was discovered
Since a supernova is the result of the collapse of a single star, due to the distances involved, it appears as one handful of bright pixels in the images obtainable with the most powerful telescopes in the world. Understand it therefore the form through images alone it is practically impossible. However, light has other characteristics besides its intensity, such as polarizationor the direction in which electric and magnetic fields oscillate which constitute light. Polarization is a property of light observable in all wavelengths of the electromagnetic spectrum. The light from the Sun and other stars is not polarized as it oscillates in all directions. Cell phone and television screens emit polarized light, which is light that has a preferred direction of oscillation.
The technique of spectropolarimetry is able to provide information on explosion geometry which other types of observation cannot provide because the angular scales are too small. Although the exploding star appears as a single point, the polarization of its light carries hidden clues about its geometry. The only instrument capable of performing spectropolarimetric measurements in the Southern Hemisphere is FORS2 installed on the VLT. If there geometry of the explosion had been sphericalthen the instrument would have observed a net polarization of the object equal to zerosince the circular symmetry would have canceled out the polarization of the individual photons between them. However, since the measured net polarization was different from zeroastronomers have thus deduced that theobject would not have spherical symmetrybut rather axialwith the initial explosion of material being shaped like an olive.
