Cosmic Ray Mystery Nearing Resolution by Astrophysicists

Astrophysicists at Michigan State University are making significant strides in resolving the century-old mystery of cosmic rays, the most energetic particles in our galaxy. Shuo Zhang, an assistant professor of physics and astronomy at MSU, along with her research team, has conducted two pivotal studies that shed light on the origins of these enigmatic particles, which have remained unclassified since their discovery in 1912.

Cosmic rays, known to travel at speeds approaching that of light, are believed to originate both from within the Milky Way and from more distant cosmic phenomena. Their exact points of origin have long puzzled scientists.

During the 246th meeting of the American Astronomical Society in Anchorage, Alaska, Zhang emphasized the relevance of cosmic rays to life on Earth, stating that around one hundred trillion cosmic neutrinos from far-off sources like black holes pass through the human body every second.

The research team is particularly focused on extreme environments such as black holes, star-forming regions, and remnants of supernovae, which are capable of generating these high-energy particles. Zhang's group is investigating natural accelerators, termed PeVatrons, which can propel protons or electrons to energies that exceed those achieved by the most advanced human-made particle accelerators.

In their first study, postdoctoral researcher Stephen DiKerby examined a high-energy source detected by the Large High Altitude Air Shower Observatory, or LHAASO, and identified it as a pulsar wind nebula using data from the XMM-Newton space telescope.

This classification adds to the limited number of identified PeVatrons. Meanwhile, undergraduates Ella Were, Amiri Walker, and Shaan Karim conducted additional observations using NASA's Swift X-ray telescope, focusing on several lesser-studied LHAASO sources.

Their findings, which calculate upper limits for X-ray emissions, aim to provide a comprehensive catalog of cosmic ray sources for future research. Zhang stated that the goal is to create a legacy that can guide future studies in particle acceleration mechanisms.

Looking ahead, the team plans to merge data from the IceCube Neutrino Observatory with X-ray and gamma-ray observations to further investigate cosmic ray sources. This collaborative effort will seek to understand the conditions under which some cosmic ray sources emit neutrinos while others do not.

This research is backed by several NASA observation grants and the National Science Foundation IceCube analysis grant, indicating strong institutional support for the endeavor. As Zhang concluded, this project represents an ideal intersection of particle physics and astronomy, underscoring the importance of interdisciplinary collaboration in tackling these fundamental cosmic mysteries.