An international team of scientists has made a groundbreaking discovery by detecting a unique signal in the radio band from a galactic black hole system. The researchers observed a galactic microquasar called GRS 1915+105 and used an advanced telescope in China for their observations. For the first time in microquasar systems, they identified a quasi-periodic oscillation (QPO) signal in the radio band, shedding light on a phenomenon previously only observed in X-rays from such systems. This finding may offer the first evidence of a “jet” launched by a galactic stellar-mass black hole, a remarkable feature that has long intrigued scientists.

Black holes are enigmatic entities with features that seem to belong in science fiction. Stellar-mass black holes, approximately ten times the mass of our sun, reveal their presence by consuming material from their companion stars. On a much grander scale, supermassive black holes, with masses equivalent to millions or even billions of suns, reside at the centers of galaxies and manifest as luminous compact regions known as quasars. A specific subset of stellar-mass black holes, known as microquasars, can emit jets of highly magnetized plasma.

The scientists, including astrophysicist Bing Zhang from the University of Nevada, Las Vegas, focused their efforts on GRS 1915+105, a galactic microquasar. Using the colossal Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China, they made a groundbreaking observation: they detected a QPO signal in the radio band from this microquasar. This signal had previously only been observed in X-rays from similar systems. The peculiar QPO signal exhibited a periodicity of approximately 0.2 seconds or a frequency of about 5 Hz. This signal’s existence is not continuous, appearing only under specific physical conditions, and the researchers were fortunate enough to capture it twice, in January 2021 and June 2022.

According to Zhang, the detected QPO signal’s unique characteristics may provide the first evidence of a “jet” launched by a galactic stellar-mass black hole. These jets, composed of charged matter and magnetic fields moving at nearly the speed of light, have remained enigmatic, and understanding the mechanism behind the temporal modulation in a relativistic jet is a significant scientific challenge. Zhang suggests a potential cause of this effect could be a misalignment between the black hole’s spin axis and its accretion disk. Nonetheless, further observations of GRS 1915+105 and other galactic microquasars will be essential in unraveling the mysteries of these intriguing QPO signals and shedding more light on the behavior of black holes in the universe.

The groundbreaking research was published in Nature.

References

• Tian, P., Zhang, P., Wang, W., Wang, P., Sun, X., Liu, J., Zhang, B., Dai, Z., Yuan, F., Zhang, S., Liu, Q., Jiang, P., Wu, X., Zheng, Z., Chen, J., Li, D., Zhu, Z., Pan, Z., Gan, H., … Sai, N. (2023). Subsecond periodic radio oscillations in a microquasar. Nature, 1–5. https://doi.org/10.1038/s41586-023-06336-6
• University of Nevada Las Vegas. (2023, July 27). Mysterious QPO Signals Reveal New Features of Galactic Black Holes. SciTechDaily. https://scitechdaily.com/mysterious-qpo-signals-reveal-new-features-of-galactic-black-holes/