Stellar mass

Stellar mass is the amount of matter gravitationally bound in a star. It shapes a star’s structure, evolution, and ultimate fate.

Hydrostatic equilibrium: A state in which inward gravity is balanced by outward pressure within an object. A star’s mass determines the gravitational load that internal pressure must support.
Binary star: A system of two stars gravitationally bound to each other. Orbital motion in binary systems provides the most direct stellar-mass measurements.
Red giant: A luminous, expanded star that has exhausted hydrogen in its core. Low- and intermediate-mass stars expand into giant phases as their cores evolve.
Stellar radius: The distance from a star’s center to its visible surface. Radius measures size, while stellar mass measures the matter bound in the star.
Solar mass: A unit of mass equal to the mass of the Sun, used for stars and other astronomical objects. Stellar masses are commonly reported as multiples of this reference unit.
Stellar structure: The internal arrangement of a star’s layers, energy sources, and physical conditions. Mass controls the pressure, temperature, and density profiles inside a star.
Kepler's laws of planetary motion: Relations describing the orbits of bodies bound by gravity, including the period–size relation. Orbital periods and separations yield component masses in binary stars.
White dwarf: A compact stellar remnant supported against gravity by electron degeneracy pressure. Stars below the threshold for core collapse typically end as white dwarfs.
Stellar luminosity: The total energy a star emits per unit time. Luminosity correlates with mass but is not itself a measure of matter.
Newton's law of universal gravitation: A law stating that two masses attract with a force proportional to their product and inversely proportional to distance squared. Its gravitational force underlies dynamical estimates of stellar mass.

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