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How do a globular cluster’s core radius and tidal radius describe its structure?

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Dense cluster of thousands of stars forming a bright, spherical shape in the night sky, representing globular cluster M13. — Globular cluster Globular cluster M13.

In the study of stellar dynamics, the structure of a globular cluster can be precisely described using two key parameters derived from dynamical models, such as those developed by the astronomer Ivan R. King:12

Core radius: This measurement quantifies the degree of stellar concentration at the center of the cluster. It reflects how tightly packed the stars are within the innermost region.12
Tidal radius: This measurement defines the outer boundary of the cluster by identifying where the density of stars drops off. It effectively marks the cutoff point of the cluster, which is determined by the gravitational tidal effects exerted by the Galaxy.12

Together, these two values allow astronomers to model the distribution of stars within a cluster, accounting for the orbits of individual stars, stellar encounters, and external gravitational influences.12