Galactic explosions, also known as supernovae, are some of the most powerful and energetic events in the universe. They occur when a star reaches the end of its life and explodes, releasing a tremendous amount of energy and matter into the surrounding space. For astrophysicists, these events offer valuable insights into the workings of the universe. They can help us understand the lifecycle of stars, the distribution of elements in the universe, and the formation of galaxies.
An international team of researchers was able to view an exploding supernova in a distant spiral galaxy by chance using data from the James Webb Space Telescope’s first year of interstellar observation.
The study, which was recently published in The Astrophysical Journal Letters, provides new infrared measurements of NGC 1566, also known as the Spanish Dancer, one of the brightest galaxies in our cosmic neighborhood. The galaxy’s extremely active center, located about 40 million light-years away from Earth, has made it especially popular with scientists seeking to learn more about how star-forming nebulae form and evolve.
In this case, scientists were able to observe a Type 1a supernova – the explosion of a carbon-oxygen white dwarf star – which Michael Tucker, a fellow at The Ohio State University and co-author of the study, said researchers discovered by chance while studying NGC 1566.
White dwarf explosions are important in the field of cosmology because astronomers frequently use them as distance indicators. They also produce a significant amount of the universe’s iron group elements, such as iron, cobalt, and nickel.
Michael Tucker
“White dwarf explosions are important in the field of cosmology because astronomers frequently use them as distance indicators,” Tucker said. “They also produce a significant amount of the universe’s iron group elements, such as iron, cobalt, and nickel.”
The research was made possible by the PHANGS-JWST Survey, which was used to create a reference dataset to study in nearby galaxies due to its vast inventory of star cluster measurements. Tucker and co-author Ness Mayker Chen, an astronomy graduate student at Ohio State who led the study, aimed to investigate how certain chemical elements are emitted into the surrounding cosmos after an explosion by analyzing images of the supernova’s core.
For instance, light elements like hydrogen and helium were formed during the big bang, but heavier elements can be created only through the thermonuclear reactions that happen inside supernovas. Understanding how these stellar reactions affect the distribution of iron elements around the cosmos could give researchers deeper insight into the chemical formation of the universe, said Tucker.
“As a supernova explodes, it expands, and as it does so, we can essentially see different layers of the ejecta, which allows us to probe the nebula’s core,” he said. Powered by a process called radioactive decay – wherein an unstable atom releases energy to become more stable – supernovas emit radioactive high-energy photons like uranium-238. In this instance, the study specifically focused on how the isotope cobalt-56 decays into iron-56.
Using data from JWST’s near-infrared and mid-infrared camera instruments to investigate the evolution of these emissions, researchers discovered that supernova ejecta was still visible at infrared wavelengths that would have been impossible to image from the ground more than 200 days after the initial event.
“This is one of those studies where it would have been very concerning if our results had not been what we expected,” he said. “We’ve always assumed that energy does not escape the ejecta, but it was only a theory until JWST.”
For many years, it was unclear whether fast-moving particles produced when cobalt-56 decays into iron-56 seeped into the surrounding environment, or were held back by the magnetic fields supernovas create.
Yet by providing new insight into the cooling properties of supernova ejecta, the study confirms that in most circumstances, ejecta doesn’t escape the confines of the explosion. This reaffirms many of the assumptions scientists have made in the past about how these complex entities work, Tucker said.
“This study validates nearly two decades of science,” he said. “It doesn’t answer every question, but it does a good job of demonstrating that our assumptions weren’t disastrously wrong.”
Future JWST observations will continue to aid scientists in developing theories about star formation and evolution, but Tucker believes that increased access to other types of imaging filters will allow them to be tested as well, providing more opportunities to learn about wonders far beyond the boundaries of our own galaxy.
“The power of JWST is truly unparalleled,” Tucker said. “It’s very encouraging that we’re doing this kind of science, and with JWST, there’s a good chance we’ll not only be able to do the same for different types of supernovas, but do it even better.”
