Researchers at Michigan State University have taken a significant step toward solving one of astrophysics’ longest-standing puzzles: the origins of galactic cosmic rays. By leveraging data from X-ray observatories and focusing on a newly identified cosmic accelerator, the team published two new studies that illuminate the elusive nature of these high-energy particles. Their findings were presented at the 246th American Astronomical Society Meeting and are detailed in The Astrophysical Journal and Research Notes of the AAS.
A Century-Old Mystery and the Power of PeVatrons
Cosmic rays, discovered in 1912, are particles—mostly protons—that travel through space at nearly the speed of light. For over a century, their exact point of origin has remained unknown. Scientists have long speculated they are born in cataclysmic events such as supernovae, black hole jets, or star-forming regions. These phenomena are also known to produce neutrinos, subatomic particles that can pass through entire planets without interacting.
Assistant Professor Shuo Zhang and her team at MSU have been investigating cosmic PeVatrons—natural accelerators capable of boosting particles to petaelectronvolt (PeV) energies, well beyond the reach of human-built accelerators. Their research focused on one of the most mysterious PeVatron candidates detected by the Large High Altitude Air Shower Observatory (LHAASO), which had not been associated with any known astrophysical object until now.
Discovery of a Pulsar Wind Nebula Sheds New Light
The team’s breakthrough came when Stephen DiKerby, a postdoctoral researcher in Zhang’s group, used data from the XMM-Newton space telescope to identify a pulsar wind nebula associated with the PeVatron candidate 1LHAASO J0343+5254u. A pulsar wind nebula is an expanding cloud of particles energized by a spinning neutron star, or pulsar. This discovery is one of the rare cases where scientists have successfully linked a PeVatron with a known class of astrophysical object.
“Cosmic rays are a lot more relevant to life on Earth than you might think,” Zhang said. “About 100 trillion cosmic neutrinos from far, far away sources like black holes pass through your body every second. Don’t you want to know where they came from?”
By confirming the presence of this nebula, the researchers were able to provide strong evidence that pulsar wind nebulae can indeed function as PeVatrons. This insight offers a new framework for tracing cosmic rays and neutrinos back to their energetic birthplaces.
Expanding the Cosmic Catalog With Student-Led X-Ray Studies
In a complementary effort, three undergraduate students from Zhang’s group—Ella Were, Amiri Walker, and Shaan Karim—conducted an X-ray survey of additional PeVatron candidates using NASA’s Swift telescope. Though the sources were faint or undetected, the team calculated upper limits for X-ray emissions, helping to narrow down possible emission scenarios. Their findings, published in Research Notes of the AAS, serve as a foundation for more targeted future studies.
“Through identifying and classifying cosmic ray sources, our effort can hopefully provide a comprehensive catalog of cosmic ray sources with classification,” Zhang said. “That could serve as a legacy for future neutrino observatories and traditional telescopes to perform more in-depth study of particle acceleration mechanisms.”
This initiative not only contributes valuable data but also underscores the role of early-career scientists in advancing high-energy astrophysics. The methodology demonstrated by the MSU team could be scaled up into a systematic survey of the sky, integrating findings from multiple observatories and wavelengths.
Next Frontier: Linking Cosmic Rays and Neutrinos
The next phase of the research will involve correlating X-ray and gamma-ray data with neutrino detections from the IceCube Neutrino Observatory in Antarctica. The goal is to uncover why some cosmic ray sources produce neutrinos while others do not. This will require cross-disciplinary collaboration between fields that often operate separately: particle physics and astronomy.
“This work will call for collaboration between particle physicists and astronomers,” Zhang said. “It’s an ideal project for the MSU high-energy physics group.”
By combining datasets across different observatories, the researchers hope to isolate the mechanisms of neutrino generation, revealing not only where they form but also how the universe’s most extreme environments operate. This kind of work could lead to new understanding in areas ranging from galactic evolution to the nature of dark matter.
