A nearby supernova that occurred in 2023, known as SN 2023ixf in the Pinwheel galaxy, provided astrophysicists a chance to study how these explosive events accelerate particles known as cosmic rays to near light-speed. Typically, supernovae were thought to convert around 10% of their energy into cosmic rays, but observations of SN 2023ixf showed a much lower conversion rate of around 1%. This discovery indicates that there is still much to learn about the process of cosmic ray production in supernovae. The findings will be published in an upcoming edition of Astronomy and Astrophysics.
Cosmic rays are high-energy particles that collide with Earth’s atmosphere on a daily basis, with the majority being hydrogen nuclei or protons, and the rest consisting of electrons or heavier elements. These particles have been a source of interest for scientists since the early 1900s, but their origin cannot be directly traced due to their interactions with magnetic fields as they travel to Earth. While cosmic rays create gamma rays when they interact with their environment, the absence of high-energy gamma-ray light from SN 2023ixf detected by NASA’s Fermi Gamma-ray Space Telescope poses a mystery that scientists aim to solve to gain a better understanding of cosmic ray origins.
Supernovae, which occur when a massive star exhausts its fuel and undergoes a core collapse followed by a rebounding shock wave, have long been suspected as major contributors to cosmic rays. These explosive events affect a galaxy’s interstellar environment for thousands of years, with remnants accelerating cosmic rays and generating gamma-ray light upon collision with interstellar matter. However, scientists have found that the remnants do not produce enough high-energy particles to match measurements on Earth. There is a theory suggesting that supernovae may accelerate the most energetic cosmic rays in the early stages after an explosion, but the rarity of these events poses challenges for direct observations.
The absence of gamma rays from SN 2023ixf does not necessarily mean there are no cosmic rays present, but rather requires a deeper investigation into the underlying factors affecting gamma-ray detection. Different scenarios such as the distribution of debris from the explosion and the density of material surrounding the star may have influenced Fermi’s observations. By studying the conditions immediately following the supernova explosion, scientists hope to gain insights that will help them refine models and simulations to better understand the sources of cosmic rays in the universe. Additional observations of SN 2023ixf at different wavelengths, as well as future studies of other young supernovae, will provide further data to advance our knowledge in this field.
Supernovae are rare events, occurring only a few times a century in a galaxy like the Milky Way. On average, a supernova takes place once a year up to a distance of 32 million light-years. Due to the infrequency of these explosions, the researchers emphasize the importance of studying SN 2023ixf to gather valuable data about cosmic ray production and acceleration mechanisms. By refining their understanding of these processes, astronomers can make strides in unveiling the mystery behind the sources of cosmic rays in the vast universe. The findings from Fermi’s observations of SN 2023ixf offer a unique opportunity to deepen our knowledge of cosmic ray origins and their interactions with supernovae.
