Black hole blinked with a radio flare express
A black hole paired with a star works like a pump: it pulls gas from its companion, swirls it into a glowing disk, and occasionally ejects some of that matter in two narrow jets. In 2021, the system 4U 1543-475 put on such a show. Radio telescopes caught two short radio bursts — traces of ejections that astronomers attribute to the black hole, though in reality they are jets born near it.
In the same days, X-ray telescopes noticed that the emission became harder: the thermal glow of the disk was joined by a contribution from a cloud of hot electrons — the corona. The reflection of this hard light from the inner parts of the disk weakened by a factor of three to four. That means the geometry of the inner flow changed for a short time: the disk may have receded, and the corona may have puffed up. Optical observations also showed variability similar to the reflected component.
The exact sequence of events could not be established: there were not enough simultaneous data. But one thing is clear: the jet does not live on its own. It is born when the disk and corona reconfigure. 4U 1543-475 gave a rare chance to see this reconfiguration simultaneously in radio, X-ray, and optical bands.
Original abstract
as written by the authors arXiv:2608.11774v1
We present a comprehensive multi-wavelength study of the black hole X-ray binary 4U 1543-475 during its 2021 outburst, focusing on radio flaring episodes that are commonly interpreted as signatures of episodic jet production and are embedded within states when the X-ray emission was dominated by an accretion disk component. The radio monitoring reveals at least two discrete flares that coincide with periods of enhanced Comptonized X-ray emission. Broadband spectral modelling shows a significant decrease in the reflection-to-disk flux ratio (by a factor of ~3-4) during these episodes, consistent with a temporary change in the geometry of the inner accretion flow, although the data do not allow the causal sequence to be firmly established. Optical photometry exhibits variability that broadly tracks the reflection fraction, consistent with changes in the illuminating component. The accompanying spectral hardening indicates that the radio flares were associated with short-lived excursions toward a "harder" state, departing from the soft state. X-ray timing analysis suggests that the radio flares may be associated with changes in the fractional rms variability; however, no consistent or unified pattern can be firmly established across different events. These results provide a multi-wavelength observational example of radio flaring activity in a black hole binary and highlight the complex interplay between accretion flow geometry, coronal emission, and jet-related phenomena.
The distance to 4U 1543-475 is about 24,000 light-years, and the 2021 outburst was noticed even by small amateur telescopes: the system brightened in optical light.
In Interstellar, the black hole Gargantua is surrounded by an accretion disk, and its glow changes as the heroes approach — similar to the variability astronomers catch in real binary systems.