In 2017, detectors picked up a tremor in space — gravitational waves from the merger of two neutron stars. At the same moment, telescopes saw a flash. For the first time, one event spoke in two languages at once: light and gravity. But the longer astronomers watched the fading glow, the stranger its behavior became.
Usually, such a collision produces a narrow jet — a beam of particles traveling at nearly the speed of light. If the jet is pointed away from us, its light should fade quickly as it expands. Here, things were different: the brightness declined very gradually. As if something kept illuminating the expanding cloud from within. This didn't fit the picture of a straight beam.
The authors of the study proposed that the jet wasn't stationary. It wobbled, like a garden hose under high pressure, tracing a glowing ring across the sky. Over time, we see a longer arc of this ring — which is why the light fades so slowly. Computer simulations showed that such a 'wobbling' jet explains the observations 4.8 times better than a rigid narrow beam.
This isn't just solving one event. Slow fading has been seen in other gamma-ray bursts as well. If wobbling jets are common, our understanding of the most powerful explosions in the Universe is about to become much more dynamic.
as written by the authors arXiv:2605.13719
GW170817 remains the only binary neutron star merger detected through multimessenger emission. Its afterglow has been monitored for nearly a decade, offering an unprecedented opportunity to probe the properties of the outflow. The shallow decay of the very late-time afterglow challenges the prediction of a collimated structured jet. Motivated by recent general-relativistic magnetohydrodynamic simulations, we propose that the GW170817 afterglow is powered by a wobbling jet that drags a ring on the sky. This structure predicts a post-break decay rate shallower than that of a collimated jet, as observers will see a progressively longer emitting arc after the break. A misaligned ring-shaped jet can therefore self-consistently explain the multimessenger data without invoking any extra component. Through a Bayesian analysis of the multimessenger data, we find a ring-shaped jet is favored over a collimated jet at a significance level of 4.8$$\sigma$$. Our results imply a wobbling angle of $$\sim 27^\circ$$. Such a large angle points to a significant disk tilt, potentially arising from disk-infalling gas interaction or asymmetric angular momentum ejection. Similar shallow decays have also been found in other GRB afterglows, raising the possibility that wobbling jets are common among GRBs.
If such a wobbling jet shone in visible light, a distant observer would see not a point but a gradually brightening and dimming ring, a cosmic 'donut' the size of the full Moon.
In Arthur C. Clarke's novel '2010: Odyssey Two', a mysterious ring on a moon of Jupiter turns out to be a gateway to other worlds — here, the ring is drawn by the physics of the explosion itself.