Black Holes as Cosmic Ray Sources: New Observations Illuminate the Galaxy’s High-Energy Puzzle
For decades, scientists have sought to understand the origin of cosmic rays - high-energy particles bombarding Earth from beyond our solar system.A especially intriguing feature of the cosmic ray spectrum is the “knee,” a sharp change in its energy distribution. recent findings, bolstered by data from the Large High Altitude Apparatus (LHAASO), are establishing a compelling link between this galactic feature and powerful black hole systems known as microquasars, fundamentally shifting our understanding of cosmic ray acceleration within the Milky Way.
These microquasars, binary systems where a black hole actively draws matter from a companion star, are known to generate intense relativistic jets. These jets accelerate particles to incredibly high energies. Observations of systems like SS 433 and V4641 Sgr have revealed gamma ray emissions reaching energies of up to 0.8 PeV, suggesting the presence of protons exceeding 10 PeV. These energies were previously considered improbable within our galaxy,positioning microquasars as strong candidates for contributing to the highest energy components of cosmic rays.
Pinpointing the sources of these high-energy particles, however, required a precise measurement of the proton spectrum – a notoriously challenging task.Space-based detectors lack the necessary sensitivity at these energies, while ground-based observations are hampered by atmospheric interference that complicates the identification of protons versus other nuclei.
LHAASO overcame these challenges through a novel, multi-parameter method, achieving an unprecedented level of purity in its proton sample. this allowed for a detailed and reliable measurement of the proton spectrum in the “knee” region,rivaling the precision of space missions. The resulting analysis revealed a surprising complexity: the transition at the “knee” isn’t a simple shift in energy distribution, but rather the emergence of a new, high-energy component. This suggests multiple sources contribute to the overall cosmic ray spectrum, with more powerful accelerators – like microquasars - dominating at PeV energies.
By integrating LHAASO’s findings with data from the AMS-02 and DAMPE missions, which focus on lower and intermediate energies respectively, a extensive picture is emerging. The Milky Way’s cosmic ray landscape isn’t shaped by a single type of accelerator, but by a diverse range of objects, each leaving its unique energetic fingerprint. The “knee” now appears to represent the maximum acceleration capability of the sources responsible for the high-energy component, specifically microquasars.
crucially, these black hole systems demonstrate an ability to accelerate protons to significantly higher energies than supernovae, the traditionally favored source of cosmic rays. This observation establishes a direct connection between a specific feature of the cosmic ray spectrum and a particular type of astrophysical object. This breakthrough highlights the power of LHAASO’s innovative design, capable of detecting both extreme gamma rays and precisely measuring particles reaching Earth.
These discoveries reveal a fundamental link between black holes and the origin of cosmic rays, offering new insights into the dynamics of the most energetic phenomena in our galaxy and marking a meaningful advancement in solving a long-standing mystery in astrophysics. The research has been published in Science Bulletin.
