A preprint posted to arXiv in April 2026 (not yet peer-reviewed) reports on a 100 ks observation using the XRISM Resolve spectrometer targeting the Ophiuchus galaxy cluster, which hosts the largest known radio bubble inflated by an active galactic nucleus (AGN). The study measures gas motions in the bubble's wake, detecting a bulk velocity shift of -80±20 km/s from the cluster center and an increase in velocity dispersion (a proxy for turbulence) from 135±10 km/s to 210±20 km/s. These findings are consistent with a buoyant updraft or "splash" of gas rising behind the bubble. The authors note the low bulk velocity implies the bubble's trajectory is significantly inclined to our line of sight.

This single-cluster, single-pointing dataset has clear limitations: it relies on spectral fitting assumptions, projection effects along the line of sight could bias results, and generalizations beyond Ophiuchus require caution. Yet the implications are striking. The turbulent kinetic energy comprises only 1% of the thermal energy radiated over the core's 7 Gyr cooling timescale and falls short by a factor of five relative to the bubble's rise time. Turbulent dissipation itself lags the core's cooling luminosity by a factor of roughly three.

Synthesizing this with the 2016 Hitomi satellite observations of the Perseus cluster core (Hitomi Collaboration, Nature, arXiv:1607.04476), which similarly found turbulence supplying just a few percent of needed heat, and theoretical models of bubble evolution (e.g., Churazov et al. simulations showing buoyant bubbles and associated wakes), a clear pattern emerges that much prior coverage has missed: even the most powerful AGN outbursts produce remarkably modest stirring. Traditional narratives emphasizing "self-regulated feedback" via turbulent reheating appear overstated.

The unexpected "splash" feature illuminates hydrodynamics others have overlooked. Rather than robust mixing, the wake suggests energy injection is inefficient at preventing runaway cooling. On cosmic scales, AGN feedback governs whether massive galaxies continue forming stars or become "red and dead." If turbulence alone cannot offset cooling, additional mechanisms—cosmic-ray streaming, sound waves, or viscous dissipation—likely play larger roles, or feedback must operate in bursty, multi-episode cycles. This work therefore reframes our understanding of galaxy evolution: the largest bubbles on the sky may be less effective governors than their size implies, forcing theorists to incorporate more nuanced coupling between supermassive black holes and their surrounding intracluster medium.