| Abstract: Radiative turbulent mixing layers are widely invoked to explain the survival, growth, and entrainment of cold gas in hot astrophysical flows, but quantitative dynamical tests have remained scarce. RBH-1, the first confirmed runaway supermassive blackhole, offers a rare opportunity to test this framework: JWST observations show a 62 kpc tail of cold H𝛼 and [OIII]-emitting gas behind a source moving at∼950 km s−1 through the hot circumgalactic medium, with a coherent velocity gradient of ∼200 km s−1 along the tail. Using 3D hydrodynamical simulations together with turbulent mixing-layer theory, I model the coherent downstream tail. I will show that the observed downstream deceleration is well reproduced by accretion-induced drag from radiative mixing layers, and that without radiative cooling no coherent cold tail forms. I will also derive a direct connection between the tail deceleration and the cooling luminosity, yielding predictions for future measurements of the cooling luminosity profile. RBH-1 therefore provides a rare quantitative dynamical stress test of radiative mixing-layer physics in an astrophysical system. |