For decades, scientists have puzzled over a cosmic riddle: the 'knee' in the cosmic ray energy spectrum. Now, groundbreaking research from China's Large High Altitude Air Shower Observatory (LHAASO) may have finally cracked the code!
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 from LHAASO revealed a sharp decrease, or 'knee,' in the cosmic ray energy spectrum above 3 peta-electronvolts (PeV).
But what exactly is this 'knee,' and why is it so important? Think of cosmic rays as high-energy particles constantly bombarding Earth from outer space. The 'knee' represents a significant change in their energy distribution, and understanding its origin could unlock secrets about the universe's most energetic processes.
Scientists have long suspected that the 'knee' is related to the acceleration limits of cosmic ray sources. The new studies, published in National Science Review and Science Bulletin, point to micro-quasars powered by black hole systems as the likely culprits. These micro-quasars, formed when black holes pull in material from companion stars, generate powerful jets that accelerate particles to near light-speed.
LHAASO's observations mark a significant leap forward. The observatory, located in Daocheng county, Southwest China's Sichuan Province, has, for the first time, systematically detected ultra-high-energy gamma rays from five micro-quasars. The results suggest that the primary cosmic rays generating these gamma rays may have energies exceeding 1 PeV, or even 10 PeV, surpassing the energy threshold of the 'knee' region. This finding addresses a long-standing issue that the previously recognized cosmic ray sources, such as supernova remnants, couldn't surpass this threshold either observationally or theoretically.
And this is the part most people miss: precise measurements of the energy spectra of various cosmic ray species are essential to understand the phenomenon. However, due to the rarity of cosmic rays in the 'knee' region and atmospheric interference, distinguishing protons from other nuclei was very challenging and once considered impossible.
LHAASO's advanced techniques allowed the team to obtain a large statistical sample of high-purity protons, revealing a new, unexpected structure in the energy spectrum: a new 'high-energy component.' This, combined with low and intermediate-energy components measured by space-borne experiments, suggests multiple accelerator populations within the Milky Way, each with unique capabilities. The 'knee' marks the acceleration limit of the sources generating the high-energy component.
But here's where it gets controversial... The findings link the 'knee' structure to a specific type of astrophysical source: a black hole jet system. According to Cao Zhen, an academician of the Chinese Academy of Sciences (CAS) and chief scientist of LHAASO, there are an estimated dozen such sources in our galaxy.
Cao also highlights the potential for these findings to impact the development of next-generation particle accelerators, as the underlying mechanisms of cosmic ray acceleration share similarities with artificial accelerators.
LHAASO, a testament to Chinese scientific innovation, is at the forefront of high-energy cosmic ray research. Its unique design allows for both gamma-ray astronomical exploration and precise cosmic ray measurement, leading to discoveries that reshape our understanding of the universe.
What do you think? Do you find the connection between black holes and cosmic rays surprising? Are you excited about the potential for these discoveries to impact other fields of science? Share your thoughts in the comments below!
