China’s cosmic ray observatory uncovers thriller of cosmic ‘knee’

An aerial drone picture taken on October 28, 2025 reveals a view of the Large High Altitude Air Shower Observatory (LHAASO) in Daocheng county, Southwest China’s Sichuan Province. Photo: Xinhua

A joint crew of Chinese and worldwide scientists launched the newest scientific outcomes from China’s Large High Altitude Air Shower Observatory (LHAASO) on Sunday. The information solved a decades-old thriller in regards to the cosmic ray vitality spectrum, which reveals a pointy lower—or a “knee”—above 3 peta-electronvolts (PeV).

The reason for the “knee” has remained unclear since its discovery almost 70 years in the past. Scientists have speculated that it’s linked to the acceleration restrict of the astrophysical sources of cosmic rays and displays the transition of the cosmic ray vitality spectrum from one power-law distribution to a different. 

Two research – revealed in National Science Review and Science Bulletin, respectively – exhibit that micro-quasars pushed by black gap system accretion are highly effective particle accelerators within the Milky Way and are the probably supply of the “knee.” The research additionally advance the understanding of the acute bodily processes of black gap techniques, the Global Times discovered on Sunday from the Institute of High Energy Physics, Chinese Academy of Sciences (CAS). 

Black holes, among the many most enigmatic objects within the universe, generate close to light-speed jets when pulling in materials from companion stars in binary techniques, forming micro-quasars. In this examine, LHAASO systematically detected ultra-high-energy gamma rays from 5 micro-quasars for the primary time. 

Results recommend that the first cosmic rays producing these gamma rays might have energies exceeding 1 PeV and even 10 PeV— surpassing the vitality threshold of the “knee” area. This discovering addressed the long-standing concern that the beforehand acknowledged cosmic ray sources, corresponding to supernova remnants, could not surpass this threshold both observationally or theoretically. 

To additional perceive the phenomenon, exact measurements of the vitality spectra of varied cosmic ray species and their respective “knee” areas are important. However, because of the rarity of cosmic rays within the “knee” area and atmospheric interference, distinguishing protons from different nuclei was very difficult and as soon as thought of unimaginable.

Based on LHAASO’s multiparameter measurement strategies, the analysis crew obtained a big statistical pattern of high-purity protons with precision akin to that of satellite tv for pc experiments. This measurement revealed a brand new construction within the vitality spectrum that was fully sudden, clearly displaying a brand new “high-energy component.”

LHAASO’s new findings, along with the low-energy part and the intermediate-energy part measured by the space-borne experiments, revealed the existence of a number of accelerator populations throughout the Milky Way, with every possessing its personal distinctive acceleration functionality and vitality vary. The “knee” represents the acceleration restrict of the sources chargeable for producing the high-energy part.

These two discoveries assist one another, presenting a complete scientific image. This not solely marks a big development in resolving the long-standing thriller of the “knee” origin, but in addition gives essential observational proof for understanding the position of black holes within the origin of cosmic rays.

According to Cao Zhen, an academician of the CAS and chief scientist of LHAASO, the power’s hybrid detector array design permits for the detection of cosmic ray sources by way of ultra-high-energy gamma rays, whereas enabling exact measurement of cosmic ray particles within the neighborhood of the photo voltaic system. 

For the primary time, the “knee” construction has been observationally related to a selected sort of astrophysical supply – a black gap jet system. It is estimated there are a dozen or so such sources in our Galaxy, Cao instructed the Global Times on Sunday. 

Cao added that the working rules of some synthetic accelerators are just like these of cosmic ray accelerations, and understanding these mechanisms has the potential to be utilized within the subsequent era particle accelerators.

LHAASO, a ground-based cosmic ray observatory designed, constructed and operated by Chinese scientists, is positioned at a excessive altitude of 4,410 meters on Mount Haizi in Daocheng county, Southwest China’s Sichuan Province. It has taken the lead in high-energy cosmic ray analysis as a consequence of its sensitivity in each gamma-ray astronomical exploration and cosmic ray precision measurement, and has achieved a sequence of discoveries with world affect, contributing to human’s understanding of the acute bodily processes within the universe.