⚛️ Where do these particles passing through your body every second come from?

Every second, without you knowing it, thousands of billions of invisible particles pass through your body. These cosmic objects travel across the Universe from distant sources, moving at prodigious speeds. For over a century, scientists have sought to understand where these particles come from and what gives them such extraordinary energy.

Cosmic rays are extremely energetic particles that travel through space at speeds close to that of light. Discovered in 1912, they originate from different regions of our galaxy and beyond, but their precise origins have long remained elusive. A team from Michigan State University, led by Shuo Zhang, is now providing new answers to this cosmic enigma. Their recent research, presented at an astronomy conference, explores the natural accelerators that propel these particles to unimaginable energies.


These energetic particles are born in extreme cosmic environments such as black holes, supernova remnants, or star-forming regions. These astrophysical phenomena also produce neutrinos, nearly massless particles that freely pass through matter, including your body.

Shuo Zhang emphasizes that these radiations directly concern us: every second, approximately one hundred trillion cosmic neutrinos pass through our bodies without us being aware of it. This omnipresence naturally raises the question of their origin and the mechanisms that generate them.

Cosmic ray sources function as natural accelerators far more powerful than those built by humans. The research team focuses on these "PeVatrons," cosmic accelerators capable of propelling protons and electrons to phenomenal energies. Understanding their operation could shed light on fundamental questions about galaxy evolution and the nature of dark matter. This research opens new perspectives for exploring particle acceleration mechanisms in the Universe.


In a first study published in The Astrophysical Journal, Stephen DiKerby examined a PeVatron candidate detected by the LHAASO observatory. By analyzing data from the XMM-Newton telescope, he identified a pulsar wind nebula - an expanding bubble containing relativistic electrons powered by a pulsar. This discovery allowed the classification of this source as a specific type of cosmic accelerator, marking an important step in identifying the origins of cosmic rays.

Three undergraduate students contributed to a second research project using NASA's Swift space telescope. Their work established upper limits for X-ray emissions from little-explored cosmic sources. These results will serve as a foundation for future studies and contribute to the development of a comprehensive catalog of cosmic ray sources. This catalog will become a valuable resource for neutrino observatories and traditional telescopes.

The team is now preparing a new study combining data from the IceCube neutrino observatory with that from X-ray and gamma-ray telescopes. They seek to understand why some cosmic sources emit neutrinos while others do not, and to identify the conditions for the production of these particles. This collaborative approach between particle physicists and astronomers represents a promising methodological advance for uncovering the secrets of cosmic accelerators.

Neutrinos, cosmic messengers

Neutrinos are elementary particles that travel through the Universe almost without interacting with matter. Their mass is so small that it was long considered zero, and they move at speeds close to that of light. Unlike electrically charged cosmic rays that are deflected by galactic magnetic fields, neutrinos travel in straight lines from their source, making them ideal messengers for locating cosmic accelerators.

These particles are produced in nuclear reactions and radioactive decay processes occurring in the cores of stars, during supernova explosions, or in the extreme environments surrounding black holes. Their detection on Earth requires particularly sensitive instruments, such as the IceCube observatory buried in the Antarctic ice, capable of capturing the very rare interactions of neutrinos with matter.

The relationship between neutrinos and cosmic rays is particularly interesting for astrophysicists. When protons or atomic nuclei are accelerated to high energy and collide with surrounding matter or radiation, they produce neutrinos among other particles. The simultaneous detection of neutrinos and cosmic rays from the same direction in the sky therefore allows for precise identification of active cosmic sources.

The study of cosmic neutrinos opens a new observational window on the Universe, complementary to traditional electromagnetic observations. By tracking these elusive particles, scientists can probe cosmic regions otherwise inaccessible, such as the interiors of stars or the immediate surroundings of black holes, thus providing us with a more complete vision of the energetic processes that animate the cosmos.