Mysterious Cygnus Bubble may trace back to microquasar, astronomers suggest

Astronomers have suggested that the mysterious Cygnus Bubble, a vast cloud of ultra-high-energy gamma rays spanning thousands of light-years, may originate from a distant microquasar rather than the previously assumed Cygnus X star-forming region. The findings, published in The Astrophysical Journal Letters on July 21, challenge existing theories about the origins of the highest-energy cosmic rays in the Milky Way. The Cygnus Bubble has long been associated with the Cygnus X star-forming region, located approximately 4,600 light-years from Earth. However, a new study led by Zhaodong Shi of the University of Science and Technology of China proposes that the structure’s intense gamma-ray emissions might instead stem from Cygnus X-3, a microquasar situated around 31,600 light-years away. This celestial body, part of a binary system containing a compact object, either a black hole or neutron star, orbited by a normal star, exhibits periodic activity that aligns with the observed characteristics of the Cygnus Bubble. Microquasars are known for launching powerful jets or winds due to the gravitational pull of their compact companions. In the case of Cygnus X-3, the system completes an orbital cycle every 4.8 hours. Recent observations from the LHAASO experiment confirmed that this microquasar functions as a “super-PeVatron,” capable of accelerating particles to energies exceeding 30 petaelectronvolts (PeV), an energy level far beyond what is typically observed in other galactic sources. This discovery strengthens the argument that Cygnus X-3 could be responsible for the Cygnus Bubble. To explore this hypothesis, the research team developed a computational model simulating the behavior of high-energy protons emitted by Cygnus X-3 over extended periods. According to the simulation, these particles gradually spread through interstellar gas, colliding with atoms and emitting detectable gamma rays. By adjusting parameters to reflect realistic physical conditions, the model accurately replicated the overall luminosity of the Cygnus Bubble and the gradual dimming of its glow as it extends outward from the central point. The study suggests that Cygnus X-3 must channel just 1% to 3% of its available energy into particle acceleration, a relatively modest requirement that aligns with established theoretical models. Moreover, the predicted rate at which these particles disperse matches independently derived expectations, further supporting the plausibility of the scenario. This potential link between Cygnus X-3 and the Cygnus Bubble represents a rare opportunity for astronomers to observe both the source of high-energy emissions and the resulting radiation halo simultaneously. Such dual visibility offers valuable insights into the mechanisms behind cosmic ray acceleration and propagation. Nevertheless, current observational tools remain insufficient to definitively distinguish the contributions of Cygnus X-3 from those of the nearby star cluster in the Cygnus X region. Future advancements in telescope technology, such as the Cherenkov Telescope Array, ASTRI, and the proposed Large Array of Cherenkov Telescopes, are expected to provide greater resolving power. These instruments will enable scientists to more precisely identify the exact origin of the Cygnus Bubble’s emissions, potentially confirming or refuting the role of Cygnus X-3 as its primary source. Until then, the debate over the nature and origin of the Cygnus Bubble continues, driven by ongoing efforts to unravel the mysteries of the universe’s most energetic phenomena.