Top: r_h (top line) and r_h,2 (bottom line) versus time (units t_rh,i) of gas models with N = 32k, m₂/m₁ = 10 and M₂/M₁ = 0.02. r_h and r_h,2 are given in N-body units. Initially, r_h and r_h,2 have the same value, but mass segregation quickly decreases r_h,2, after which it reaches an approximately steady value. Bottom: r_h,2/r_h versus time (units t_rh,i). Core collapse (see Section 2.1) occurs at ≈1t_rh,i; shortly before this r_h,2/r_h reaches a nearly constant value.