Energy Routing Regimes and Mass Formation Thresholds: A Classification Framework with an Astrophysical Case Study

Mass formation does not occur ubiquitously in astrophysical gas, even in systems that are dense, long-lived, and strongly interacting with their environments. This indicates that density and gravitational binding alone are insufficient criteria for condensation. In this paper, we propose a classification framework based on the availability of recyclable degrees of freedom for energy routing, rather than a specific microphysical mechanism. We introduce a “degrees-of-freedom ladder” that organizes astrophysical systems according to their effective capacity to redistribute injected energy through exchange pathways, boundary mediation, or internal circulation. In this view, mass formation corresponds to a threshold at which routing freedom becomes insufficient to prevent persistent energy accumulation and structural collapse. This framework is explicitly classificatory and descriptive: it does not assert a unique mechanism for regime transitions. As a consistency test, we apply the framework to the Smith Cloud in an appendix, using published observational constraints to evaluate whether its energetics are compatible with a boundary-supported, non-condensing regime. We find that the Smith Cloud is consistent with such a regime within reasonable parameter ranges, supporting—but not proving—the broader mass-formation hypothesis advanced here.