Milky Way's New Microquasar Breaks Cosmic Ray Energy Records

A groundbreaking discovery has emerged from the Milky Way galaxy, where a microquasar named V4641 Sagittarii has shattered previous energy records for cosmic rays. Located approximately 20,000 light-years from Earth in the constellation Sagittarius, this binary star system, consisting of a massive star and a black hole, has been observed generating photons with energy levels exceeding 200 tera-electron-volts (TeV). This unprecedented finding positions V4641 Sagittarii as a significant contributor to cosmic ray production within our galaxy.

Microquasars are stellar systems that behave similarly to quasars, but on a much smaller scale. They typically consist of a normal star orbiting a compact object, such as a black hole or neutron star, which siphons material from its companion. This interaction creates an accretion disk that heats up and emits intense X-rays, while simultaneously launching high-energy particle jets that move at nearly the speed of light. According to Dr. Sabrina Casanova, a researcher at the Institute of Nuclear Physics of the Polish Academy of Sciences, the observed photon emissions from V4641 Sagittarii are astonishing because they carry energies tens of thousands of times greater than those typically emitted by microquasars, which rarely exceed a few tens of giga-electron-volts (GeV).

The High-Altitude Water Cherenkov Observatory (HAWC) in Mexico has played a pivotal role in this discovery. Utilizing a network of 300 steel tanks filled with clear water, the observatory detects gamma rays that strike the Earth's upper atmosphere, resulting in cascades of particles that produce Cherenkov radiation. This method allows HAWC to monitor cosmic rays in real time, leading to the identification of a persistent signal from V4641 Sagittarii.

Dr. Casanova highlighted, “We have observed something quite incredible … photons coming from a microquasar lying in our galaxy and yet carrying energies tens of thousands of times higher than typical!” This observation prompts a reevaluation of the sources of high-energy cosmic rays, traditionally attributed to supernova remnants. The findings suggest that compact binary systems like V4641 Sagittarii can also contribute significantly to the high-energy end of the cosmic ray spectrum.

The microquasar system comprises a black hole with a mass equivalent to approximately six Suns and a companion star with a mass of about three Suns. They orbit a common center of mass every 2.8 days, forming a tightly wound accretion disk. The black hole’s powerful magnetic fields generate jets that can extend hundreds of light-years, with one jet oriented toward Earth, creating an apparent superluminal motion nine times faster than light.

The implications of these findings extend beyond the Milky Way. The results from HAWC, along with support from China’s Large High Altitude Air Shower Observatory, indicate a broader class of microquasars that may be contributing to cosmic rays at energies beyond 100 TeV. This challenges the long-held belief that supernova explosions were the primary source of galactic cosmic rays. Instead, the detection of high-energy emissions from microquasars indicates a shift in understanding cosmic ray origins and their distribution in the galaxy.

Looking ahead, HAWC will continue to monitor V4641 Sagittarii for daily variations that could correlate gamma-ray emissions with radio flares observed by interferometers. Upcoming instruments, such as the Cherenkov Telescope Array, will enhance the observational capabilities, providing high-resolution images and searching for neutrinos that could further validate the hadronic processes at play. The study of V4641 Sagittarii not only enriches our understanding of microquasars but also opens new avenues for exploring the dynamics of high-energy astrophysical phenomena within our own galaxy. This research was published in the journal *Nature* on June 26, 2025.