Subsecond periodic radio oscillations in a microquasar

Powerful relativistic jets are one of the ubiquitous features of accreting black holes in all scales^1-3. GRS 1915 + 105 is a well-known fast-spinning black-hole X-ray binary⁴ with a relativistic jet, termed a `microquasar', as indicated by its superluminal motion of radio emission^5,6. It has exhibited persistent X-ray activity over the last 30 years, with quasiperiodic oscillations of approximately 1-10 Hz (refs. ^7-9) and 34 and 67 Hz in the X-ray band¹⁰. These oscillations probably originate in the inner accretion disk, but other origins have been considered¹¹. Radio observations found variable light curves with quasiperiodic flares or oscillations with periods of approximately 20-50 min (refs. ^12-14). Here we report two instances of approximately 5-Hz transient periodic oscillation features from the source detected in the 1.05- to 1.45-GHz radio band that occurred in January 2021 and June 2022. Circular polarization was also observed during the oscillation phase.