Observations of SN 2023ixf in 2023 led to surprising findings regarding cosmic ray production by supernovae, with potential implications for understanding cosmic ray origins and acceleration mechanisms.
In 2023, a nearby supernova offered astrophysicists an excellent opportunity to test ideas regarding how these types of explosions boost particles, called cosmic rays, to near light-speed. But surprisingly, NASA’s Fermi Gamma-ray Space Telescope detected none of the high-energy gamma-ray light those particles should produce.
On May 18, 2023, a supernova erupted in the nearby Pinwheel galaxy (Messier 101), located regarding 22 million light-years away in the constellation Ursa Major. The event, named SN 2023ixf, is the most luminous nearby supernova discovered since Fermi launched in 2008.
“Astrophysicists previously estimated that supernovae convert regarding 10% of their total energy into cosmic ray acceleration,” said Guillem Martí-Devesa, a researcher at the University of Trieste in Italy. “But we have never observed this process directly. With the new observations of SN 2023ixf, our calculations result in an energy conversion as low as 1% within a few days following the explosion. This doesn’t rule out supernovae as cosmic ray factories, but it does mean we have more to learn regarding their production.”
The paper, led by Martí-Devesa while at the University of Innsbruck in Austria, will appear in a future edition of Astronomy and Astrophysics.
Even when it doesn’t detect gamma rays, NASA’s Fermi Gamma-ray Space Telescope helps astronomers learn more regarding the universe. Cosmic rays and their origins have been a topic of investigation since the early 1900s. These charged particles, mostly hydrogen nuclei or protons, collide with Earth’s atmosphere every day. However, their sources cannot be directly traced due to the influence of magnetic fields on their trajectory.
On the other hand, gamma rays, a form of high-energy electromagnetic radiation, travel directly to us without changing their course. They are produced when cosmic rays interact with matter in their environment. By detecting gamma rays, scientists can gain insights into the sources and behaviors of cosmic rays.
Supernovae have long been suspected as major contributors to cosmic ray production. These explosive events occur when a star, at least eight times the mass of our Sun, runs out of fuel and collapses. The resulting shock wave accelerates particles, creating cosmic rays. When these cosmic rays collide with surrounding matter and light, they generate gamma rays.
Supernovae have a significant impact on a galaxy’s interstellar environment, with their blast waves and debris clouds persisting for thousands of years. Previous measurements by Fermi revealed that supernova remnants in our own Milky Way galaxy accelerate cosmic rays, producing gamma-ray light upon collision with interstellar matter. However, astronomers have faced challenges in reconciling the observed cosmic ray production with the measurements made on Earth.
One theory suggests that supernovae may accelerate the most energetic cosmic rays shortly following the initial explosion. However, supernovae are relatively rare events, occurring only a few times a century in a galaxy like the Milky Way. Therefore, the opportunity to study conditions immediately following a supernova explosion, as was the case with SN 2023ixf, provides valuable insights into the mechanisms of cosmic ray production.
The absence of gamma rays detected by Fermi regarding SN 2023ixf raises questions regarding the underlying hypotheses regarding acceleration mechanisms and environmental conditions. However, the researchers propose several scenarios that might have affected Fermi’s ability to observe gamma rays, such as the distribution of debris and the density of material surrounding the star.
Analyzing the implications of these findings leads to a broader understanding of cosmic ray origins and the factors influencing their production. By studying other young supernovae, conducting additional observations of SN 2023ixf at different wavelengths, and developing new simulations and models, astronomers can continue unraveling the mystery behind cosmic ray sources.
In the future, advancements in observational capabilities, along with improved understanding of the mechanisms involved in cosmic ray production, can lead to breakthroughs in our knowledge of the universe. Cosmic rays play a crucial role in shaping our understanding of cosmic phenomena and can provide insights into the evolution and dynamics of galaxies.
As technology continues to advance, new telescopes and instruments may enable scientists to probe deeper into cosmic ray origins and delve into more distant supernova events. These developments can potentially unveil new physics and shed light on the fundamental processes that drive the universe.
In conclusion, the surprising findings from the observations of SN 2023ixf open up new avenues of research and raise intriguing questions regarding cosmic ray production by supernovae. By
