BEIJING, May 9 (Xinhua) -- For decades, scientists have been trying to solve a mystery: Where do high-energy cosmic rays come from? These charged particles travel from outer space to Earth, but their origins remain unknown. Now, a major discovery by Chinese scientists is bringing them closer to the answer.
Based on observations from China's Large High Altitude Air Shower Observatory (LHAASO), researchers have detected ultra-high-energy gamma rays from a special type of object in the Milky Way. This object is a gamma-ray binary system, meaning it consists of two stars: one massive star and one compact object. The compact object could be either a neutron star or a black hole.
The energy of the gamma rays detected by the team is extremely high, reaching over 100 trillion electron-volts. This is far beyond what scientists had seen from this object before.
The new discovery, recently published in the journal Physical Review Letters, was led by scientists from the Institute of High Energy Physics (IHEP) under the Chinese Academy of Sciences.
According to the study, in such binary systems, the strong magnetic field around the compact object usually causes high-energy electrons to lose energy rapidly. That makes it hard for them to reach extremely high energy levels. However, the detection of gamma rays above 100 trillion electron-volts suggests that something else is happening.
According to the research team, high-energy protons are likely being accelerated in the system during certain orbital phases. These protons then crash into the dense wind coming from the massive star, producing the ultra-high-energy gamma rays.
This discovery provides strong evidence that this type of gamma-ray binary system is a potential PeVatron. A PeVatron is a natural particle accelerator in space that can push cosmic rays up to energies of one thousand trillion electron-volts. That is a hundred times higher than what the Large Hadron Collider, the most powerful human-made particle accelerator on Earth, can achieve.
The researchers also found that the brightness of the gamma rays changes with the system's orbital period, which is about 26.5 days. This pattern shows a clear dependence on energy, indicating that the physical processes within the system are complex and change as the two stars orbit each other.
This discovery is not just about one binary system. It opens a new window for understanding how the universe works on its most extreme scale, said He Huihai, a researcher from the IHEP.
"It also prepares the ground for future multi-messenger astronomy, in which scientists study the universe using not only light but also other signals such as cosmic rays and neutrinos," he added.
LHAASO, located at an altitude of 4,410 meters on Mount Haizi in Daocheng County, southwest China's Sichuan Province, is China's national key scientific and technological infrastructure focusing on cosmic ray research.
The observatory, the most sensitive ultra-high-energy gamma-ray detection device in the world, was completed in July 2021 and began operating stably and with high quality thereafter. ■
