Microquasars Identified as Primary Accelerators of Galactic Ultra-Energetic Cosmic Rays

Scientists utilizing the Large High Altitude Air Shower Observatory (LHAASO) have presented evidence identifying microquasars as the dominant accelerators responsible for the most energetic cosmic rays within the Milky Way galaxy. This finding addresses the long-standing question regarding the origin of these high-energy particles, a mystery that has persisted for nearly seven decades. Microquasars, defined as binary systems featuring a black hole actively accreting matter from a companion star, generate powerful relativistic jets that energize particles to extreme velocities.

The research, involving an international consortium including the Institute of High Energy Physics of the Chinese Academy of Sciences (CAS) and Nanjing University, was detailed in publications such as the National Science Review and Science Bulletin. The LHAASO observational campaign employed an advanced hybrid detector array, uniquely positioned to simultaneously detect ultra-high-energy gamma rays from distant sources and conduct precise measurements of cosmic ray particles near the solar system. This dual capability enabled researchers to link the "knee" in the cosmic ray energy spectrum—a sharp flux decrease observed above approximately 3 PeV—to these specific black hole jet systems.

Key data supporting this conclusion include the detection of photons with energies surpassing 1 PeV emanating from a structure within the Cygnus star-forming region, with the maximum recorded energy reaching 2.5 PeV. Further analysis of the microquasar SS 433 indicated its accelerated protons exceeded 1 PeV, with an estimated power output equivalent to the energy released by four trillion hydrogen bombs per second. Another identified accelerator, V4641 Sgr, yielded gamma-ray energies up to 0.8 PeV, confirming the presence of multiple PeV particle accelerators across the galaxy. These findings fundamentally challenge the traditional astrophysical paradigm that primarily attributed galactic cosmic ray production to supernova remnants, as theoretical models suggest these remnants lack the capacity to reach the energies associated with the knee.

The LHAASO facility, situated at an altitude of 4,410 meters above sea level on Mount Haizi in Daocheng County, Sichuan Province, China, commenced operations in April 2019 across an area of approximately 145 hectares. Lead Researcher Cao Zhen, an Academician of the CAS and the principal investigator for LHAASO, stated that these studies illuminate the primary mechanisms behind cosmic ray origins and enhance the comprehension of extreme physical processes occurring within black hole systems. The identification of approximately a dozen such microquasar sources provides tangible targets for future investigations using advanced gamma-ray and neutrino experiments, setting a new direction for high-energy astrophysics.