Kinetic heterogeneities in a highly supercooled liquid

We study a highly supercooled two-dimensional fluid mixture via molecular dynamics simulation. We follow bond breakage events among particle pairs, which occur on the scale of the alpha relaxation time tau(alpha). Large scale heterogeneities analogous to the critical fluctuations in Ising systems are found in the spatial distribution of bonds which are broken in a time interval with a width of order 0.05 tau(alpha). The structure factor of the broken bond density is well approximated by the Ornstein-Zernike form. The correlation length is of order 100 sigma(1) at the lowest temperature studied, sigma(1) being the particle size. The weakly bonded regions thus identified evolve in time with strong spatial correlations.