Mass-radius diagram for stellar systems to illustrate relevant timescales and the position of different sources in different parts of the parameter space. The red dots show LRDs from A+24, gray dots show NSCs in the local Universe (Georgiev et al. 2016; Neumayer et al. 2020), blue dots show well-resolved BHs, and orange dots show spatially unresolved BHs (Gültekin et al. 2009; Escala 2021). The solid black line represents the collisional timescale t_coll = 13.7 Gyr, and the dashed black line shows the relaxation time for t_relax = 13.7 Gyr. We include (in green) a fiducial galaxy with mass 10¹⁰ M_⊙ and radius 20 pc to show its trajectory in the mass-radius plane for β = 1 and 0.5, as defined in Eq. (3). The time evolution of the green line is from left to right.