New research from astrophysicists at Michigan State University may bring scientists closer to solving a mystery that has puzzled them for more than a century: where do galactic cosmic rays come from?

Cosmic rays are high-energy particles that travel at nearly the speed of light. They originate from locations both within the Milky Way and beyond, yet their exact sources have remained unknown since their discovery in 1912.

Shuo Zhang, an assistant professor of physics and astronomy at MSU, and her research team led two recent studies offering new insights into where these particles may have formed. The findings were presented at the 246th meeting of the American Astronomical Society in Anchorage, Alaska.

These energetic particles are believed to come from some of the universe’s most extreme environments, including black holes, supernova remnants, and regions where stars are born. Such astrophysical events also generate neutrinos, which are tiny, nearly massless particles found throughout the cosmos and even here on Earth.

“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?”

The Universe’s Ultimate Accelerators
The sources of cosmic rays are so powerful that they can accelerate protons and electrons to energy levels far exceeding what is possible with even the most advanced human-made particle accelerators. Zhang’s group focuses on these natural cosmic accelerators, known as PeVatrons, to understand where they exist, what they are made of, and how they propel particles to such extreme energies.

Gaining a deeper understanding of these mechanisms could help answer fundamental questions about galaxy evolution and the mysterious nature of dark matter.