Attractor of hydrodynamic attractors

Understanding how hydrodynamics emerges rapidly in the medium produced by relativistic heavy-ion collisions remains a key theoretical challenge. While the attractor solution – manifesting as a non-thermal fixed point during the early evolution stage – offers a potential explanation, it does not fully account for how far-from-equilibrium systems quickly approach near-equilibrium states. In this Letter, we demonstrate that the attractor in a higher-order hydrodynamic theory converges to the same solution as a second-order theory before reaching the Navier–Stokes limit. This finding suggests that commonly used second-order hydrodynamic equations, provided they incorporate the correct transport coefficients, are adequate to approximate the system’s behavior starting from an intermediate time – even when using a higher-order theory that would be more suitable for describing the far-from-equilibrium evolution.