For nearly seven decades, a peculiar bend in the cosmic ray energy spectrum—known as the 'knee'—has baffled scientists. But what if this mysterious kink holds the key to understanding the universe's most powerful particle accelerators? Recent groundbreaking findings from the Large High Altitude Air Shower Observatory (LHAASO) have finally shed light on this enigma, revealing a surprising culprit behind the cosmic ray 'knee.'
On November 16, LHAASO unveiled milestone results that point to micro-quasars—relativistic jets powered by black hole accretion in binary star systems—as the likely source of this phenomenon. This discovery, published in National Science Review and Science Bulletin, not only solves a long-standing astrophysical mystery but also deepens our understanding of the extreme physics governing black hole systems. But here's where it gets controversial: could micro-quasars, not supernova remnants, be the dominant accelerators of high-energy cosmic rays in our galaxy?
Led by researchers from the Chinese Academy of Sciences (CAS), Nanjing University, and international collaborators, the study marks the first systematic detection of ultra-high-energy gamma rays from five micro-quasars: SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070, and Cygnus X-1. Among these, SS 433 stands out: its gamma rays overlap with a giant atomic cloud, strongly suggesting that protons accelerated by the black hole collide with surrounding matter. These protons boast energies exceeding 1 PeV, releasing a staggering 10³² joules per second—equivalent to four trillion hydrogen bombs detonating every second. V4641 Sgr, another micro-quasar, accelerates particles to 0.8 PeV, further cementing their role as 'super PeV accelerators.'
These findings challenge the traditional view that supernova remnants are the primary sources of cosmic rays. While supernovae were long suspected, both theory and observation confirm their inability to accelerate particles beyond the 'knee.' LHAASO's precision measurements of proton energy spectra reveal a previously unseen 'high-energy component,' indicating that cosmic rays in the PeV range originate from 'new sources' like micro-quasars, whose acceleration limits far surpass those of supernovae.
And this is the part most people miss: LHAASO's hybrid detector array not only identifies cosmic ray sources via gamma rays but also precisely measures particles near our solar system. This dual capability has, for the first time, observationally linked the 'knee' to black hole jet systems, offering a unified picture of multiple accelerators in the Milky Way—each with unique energy ranges and capabilities.
Designed and operated by Chinese scientists, LHAASO's unparalleled sensitivity in gamma-ray astronomy and cosmic ray measurement has propelled it to the forefront of high-energy astrophysics. Its discoveries not only resolve the 'knee' mystery but also provide critical evidence for black holes' role in cosmic ray production. But the debate isn't over: do these findings redefine our understanding of cosmic ray origins, or is there more to the story? Share your thoughts below—are micro-quasars the true cosmic accelerators, or is the universe still hiding secrets?
