After more than a decade of observation, an international team of astrophysicists has confirmed that the jets of a peculiar object in our galaxy are accelerating particles to energies a hundred times greater than the most powerful particle accelerator on Earth. Using an array of specialized telescopes, researchers have detected very-high-energy gamma rays coming from the lobes of SS 433, a binary star system known as a microquasar, providing a unique laboratory for understanding extreme cosmic phenomena.
The findings represent the culmination of over 250 hours of observation by the VERITAS array in Arizona, which recorded gamma rays with energies in the teraelectronvolt (TeV) range. This detection confirms that the jets of SS 433, which are blasting streams of matter into interstellar space at 26% the speed of light, are a source of powerful cosmic rays. The study offers crucial insight into the mechanisms of particle acceleration in relativistic jets, a phenomenon observed in more distant and powerful objects like active galactic nuclei.
A Unique Celestial Laboratory
SS 433 is a remarkable system located about 18,000 light-years away in the constellation Aquila. It consists of a massive star and a compact object, likely a black hole, that is siphoning material from its companion. This stolen matter forms a superheated accretion disk around the black hole, which then expels a portion of it in two powerful, oppositely directed jets of hot hydrogen. What makes SS 433 particularly noteworthy is that its jets are precessing, meaning they wobble like a spinning top, carving out a vast, corkscrew-shaped cavity in the surrounding supernova remnant known as W50. This entire structure provides a nearby and observable example of the jet-powered systems seen at the centers of other galaxies.
Decades of Dedicated Observation
The research involved the Very Energetic Radiation Imaging Telescope Array System (VERITAS), an array of four 12-meter telescopes designed to detect the faint, brief flashes of blue light, known as Cherenkov radiation, produced when very-high-energy gamma rays strike the upper atmosphere. The array is located at the Fred Lawrence Whipple Observatory in southern Arizona. The collaboration observed SS 433 for over a decade, accumulating approximately 100 hours of exposure on the system’s eastern lobe and 150 hours on its western lobe. This long-term campaign was necessary to gather enough data to distinguish the faint gamma-ray signal from the overwhelming background of charged cosmic rays.
Advanced Analysis Techniques
Detecting the faint gamma-ray signature from the jets required sophisticated analysis. The team used advanced three-dimensional maximum likelihood techniques to analyze the spatial and spectral characteristics of the emissions. This method allowed them to pinpoint the origin of the gamma rays. The analysis revealed two elongated regions of emission that align with the jet axis on either side of the central binary system. This morphology strongly suggests that the particles are being accelerated within the jets, most likely where the jets terminate and interact with the surrounding interstellar medium of the W50 nebula.
Confirming a Cosmic Accelerator
The VERITAS observations resulted in a highly significant detection, with a combined statistical significance of 8.8 sigma from both the eastern and western jet lobes. This level of certainty firmly establishes SS 433 as a source of very-high-energy gamma rays and, by extension, a galactic particle accelerator. The results provide direct observational evidence that the jets of a microquasar can accelerate particles, in this case likely electrons and protons, to teraelectronvolt energies. This process is similar to what is believed to happen in the much larger and more powerful jets of quasars and radio galaxies, but SS 433 allows for a much more detailed study due to its relative proximity.
Implications for Cosmic Ray Origins
The study of SS 433 helps scientists understand where the universe’s most energetic particles come from. Microquasars are increasingly recognized as efficient particle accelerators that could contribute to the overall flux of cosmic rays bombarding Earth’s atmosphere. The detailed morphological and spectral measurements from VERITAS provide crucial data for modeling the precise mechanisms at play, including how energy is transferred from the jet’s kinetic power to individual particles. The findings from SS 433 serve as a critical testbed for theories of particle acceleration in astrophysical jets of all scales.
Future Research Directions
This confirmation of TeV gamma-ray emission opens new avenues for research. The high-resolution measurements, with an angular resolution of less than 0.1 degrees, allow for a detailed study of the jet lobes and the interaction zones. Future observations will aim to further resolve these structures and study how the emission varies with the 162-day precession period of the jets. By combining data from VERITAS with observations from other instruments across the electromagnetic spectrum, from radio waves to X-rays, scientists hope to build a complete picture of this extraordinary natural particle accelerator and its impact on the surrounding galactic environment.
