Astrophysics.

The entropy — and so the total information content — of any physical system is capped by its energy and physical size: S ≤ 2π k_B E R/(ℏ c) for a system with energy E confined within radius R, setting an absolute upper limit on how much information can fit in a bounded region of space.

Before neutron stars were even confirmed to exist, Chandrasekhar showed that white dwarf stars have a maximum possible mass — beyond it, electron degeneracy pressure can no longer support the star against gravitational collapse. His original 1931 calculation used an idealized, composition-independent model.

Beyond a certain mass, a neutron star's own gravity overwhelms the quantum pressure holding it up, and it collapses into a black hole. The exact maximum mass depends on the poorly-constrained neutron-star equation of state; this record cites an early rigorous bound assuming causality.

Dated high-mass pulsar measurement; it constrains but does not equal the universal neutron-star maximum.

Observed extremely low-mass white dwarfs establish a dated one-sided low-mass frontier rather than a universal minimum.

Radiative luminosity at which outward opacity force balances gravity in spherical steady flow.

Critical mass for gravitational instability in the conventional uniform isothermal Jeans analysis.

Classical disruption distance for a synchronously rotating fluid satellite on a circular orbit.

Leading-order radius of the secondary's gravitational sphere of influence in the restricted three-body approximation.

Model-inferred current mass of R136a1 in the cited analysis; revisions and multiplicity remain part of the open frontier.

Classic zero-metallicity stellar models predict complete disruption over a model-dependent helium-core mass interval.

Model-dependent lower main-sequence mass for sustained hydrogen burning near solar composition.

Upper brown-dwarf mass boundary is the same composition-dependent transition to sustained hydrogen burning.

Any reliably dated star supplies a one-sided lower bound on cosmic age, with stellar-model uncertainty retained.

Semiclassical temperature of an uncharged nonrotating black hole.

Idealized mass-cubed lifetime from blackbody Hawking power for a neutral nonrotating black hole.

Classical Kerr spacetime has an event horizon only at or below unit dimensionless spin.

Compactness bound for static spherical perfect-fluid stars satisfying Buchdahl's assumptions.

Maximum nonrotating neutron-star mass is an equation-of-state-dependent frontier, not a universal scalar.

Maximum mass in the original zero-temperature ideal neutron-gas general-relativistic model.

Maximum mass of a cold, nonrotating ideal electron-degenerate white dwarf as a function of composition.

Areal radius of the event horizon in the Schwarzschild vacuum solution.