For decades, scientists have puzzled over a cosmic riddle: the 'knee' in the cosmic ray energy spectrum. But now, a groundbreaking discovery from China's Large High Altitude Air Shower Observatory (LHAASO) is rewriting the textbooks!
On Sunday, a joint team of Chinese and international scientists unveiled their latest findings, offering a solution to a mystery that has baffled researchers for nearly 70 years. The data revealed a sharp decline, or "knee," in the cosmic ray energy spectrum above 3 peta-electronvolts (PeV). But what exactly does this mean?
Cosmic rays, high-energy particles from outer space, bombard Earth constantly. Their energy spectrum, a measure of their energy distribution, has a peculiar shape. The "knee" is where this spectrum takes a dramatic dip, and scientists have been trying to figure out why.
Scientists have long suspected that the "knee" is linked to the acceleration limits of cosmic ray sources. The LHAASO's recent research, published in National Science Review and Science Bulletin, points to micro-quasars as the likely culprits. These micro-quasars, powered by black hole systems, are powerful particle accelerators within our Milky Way galaxy.
And this is the part most people miss... Black holes, some of the most mysterious objects in the universe, create near light-speed jets when they pull in material from companion stars, forming micro-quasars. LHAASO has, for the first time, systematically detected ultra-high-energy gamma rays from five micro-quasars.
These findings suggest that the primary cosmic rays generating these gamma rays have energies exceeding 1 PeV, even reaching 10 PeV—surpassing the "knee" region's energy threshold. This discovery resolves a long-standing issue where previously identified cosmic ray sources, such as supernova remnants, couldn't reach this threshold.
To further understand the phenomenon, precise measurements of the energy spectra of different cosmic ray types are essential. LHAASO's advanced techniques allowed the team to obtain a large sample of high-purity protons with precision comparable to satellite experiments. This revealed a new, unexpected structure in the energy spectrum, showcasing a new "high-energy component."
LHAASO's new findings, combined with data from space-borne experiments, reveal multiple accelerator populations within the Milky Way, each with its unique capabilities. The "knee" represents the acceleration limit of the sources generating the high-energy component. These discoveries offer crucial observational evidence for understanding the role of black holes in cosmic ray origins.
According to Cao Zhen, an academician of the Chinese Academy of Sciences (CAS) and chief scientist of LHAASO, the observatory's design allows for the detection of cosmic ray sources through ultra-high-energy gamma rays while precisely measuring cosmic ray particles. For the first time, the "knee" structure has been linked to a specific astrophysical source: a black hole jet system. It's estimated that there are about a dozen such sources in our galaxy.
But here's where it gets controversial... Cao also mentioned that the working principles of some artificial accelerators are similar to those of cosmic ray acceleration, which could potentially revolutionize the next generation of particle accelerators.
LHAASO, located at a high altitude of 4,410 meters on Mount Haizi in Daocheng county, Southwest China's Sichuan Province, has become a leader in high-energy cosmic ray research. Its ability to explore gamma rays and precisely measure cosmic rays has led to several discoveries, enhancing our understanding of the universe's extreme physical processes.
What do you think? Does this new information change how you view black holes and their role in the cosmos? Do you think this will lead to new technologies?
