selfbound

Self-bound is an adjective used in physics, astronomy, and related fields to describe a system that remains bound due to its own internal interactions or energy, rather than because of an external confining potential or container. In some texts the term appears as selfbound or self-bound.

In physics and condensed matter, self-bound systems arise when attractive interparticle forces overcome dispersion or kinetic pressure, forming a stable finite-size object without external confinement. Examples include atomic nuclei and quantum droplets in ultracold gases, where the balance between attraction and repulsive forces or quantum fluctuations yields a self-sustained state. In these contexts, the term emphasizes that the binding energy is intrinsic to the system.

In astrophysics, many structures are described as self-bound when gravity alone provides confinement, independent of an external medium. Planets, stars, and many star clusters are self-bound by their own gravity, whereas systems in tidal or ambient pressure environments may be only loosely bound or unbound.

In chemistry and materials science, self-binding can refer to cohesive energy arising from chemical bonds that hold a material together, without needing an external matrix.

Usage and limitations: The term is sometimes used informally; in precise technical writing, more specific descriptors such as "self-bound by internal forces," "gravitationally bound," or "quantum self-bound state" are preferred.

Variants: self-bound, selfbound, and hyphenated forms appear in different sources; the preferred form depends on field and publication style.