Researchers from the High-Altitude Water Cherenkov Gamma-Ray Observatory (HAWC) have identified microquasars as a significant source of ultra-high-energy cosmic radiation. The discovery challenges long-standing views that supernova remnants were the primary accelerators of these particles. Scientists from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) played a key role in this finding, which was funded by the National Science Centre.

Located on the Sierra Negra volcano in Mexico, the HAWC observatory is designed to detect incoming high-energy particles from space. It uses 300 water tanks equipped with photomultipliers to capture Cherenkov radiation, allowing it to observe gamma photons with energies ranging from hundreds of gigaelectronvolts to teraelectronvolts. These gamma rays are far more energetic than visible light and even more powerful than protons accelerated by the Large Hadron Collider.

Typically, quasars - found in the nuclei of distant galaxies - are known for producing such high-energy radiation through jets of matter expelled by supermassive black holes. However, microquasars, which consist of a massive star and a black hole, can generate similarly powerful jets on a smaller scale. Several dozen microquasars have been identified within the Milky Way, with their jets extending for hundreds of light years.

Dr. Sabrina Casanova from IFJ PAN, along with Dr. Xiaojie Wang from Michigan Tech University and Dr. Dezhi Huang from the University of Maryland, led the research team that first detected an anomaly in HAWC's data - gamma photons from the microquasar V4641 Sagittarii (V4641 Sgr) carrying energies up to 200 teraelectronvolts. V4641 Sgr is located in the constellation Sagittarius, about 20,000 light years from Earth. Its jets, pointed towards our Solar System, create the illusion of moving faster than light due to relativistic effects, making it appear to travel at nine times the speed of light.

Dr. Casanova noted, "Photons detected from microquasars have usually much lower energies than those from the quasars. Meanwhile, we have observed something quite incredible in the data recorded by the detectors of the HAWC observatory: photons coming from a microquasar lying in our galaxy and yet carrying energies tens of thousands of times higher than typical!"

This groundbreaking discovery highlights that V4641 Sgr is not unique. Other microquasars, observed by the LHAASO observatory, also emit similarly powerful radiation. The study suggests that microquasars may significantly contribute to cosmic radiation within our galaxy.

Dr. Casanova added, "It therefore seems likely that microquasars significantly contribute to the cosmic ray radiation at the highest energies in our galaxy."

These new insights are not only important for cosmic ray research but also provide astronomers with an opportunity to study high-energy processes close to Earth. Unlike quasars in distant galaxies, which can take millions of years to evolve, the jets from microquasars can be observed in real-time over days. Moreover, the radiation from these nearby objects does not have to travel through vast intergalactic distances, where it can be scattered or absorbed, allowing for clearer observations.

Research Report:"Ultra-high-energy gamma-ray bubble around microquasar V4641 Sgr"

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