Definition
A dwarf star is a stellar object with relatively small mass, characterized by compact size and moderate or low brightness. The term includes several types of stars at different evolutionary stages: white dwarfs, red dwarfs, brown dwarfs, and sometimes yellow dwarfs. Each has its own features, but all are smaller than massive stars.
Types and Structure
Red dwarfs are active fusion stars with low mass and temperature, possessing a convective core that allows long-term hydrogen burning. White dwarfs are very dense stellar remnants, mainly composed of carbon and oxygen, with no nuclear reactions. Brown dwarfs, often called failed stars, do not reach the required mass to start fusion and consist mainly of compressed gas. Yellow dwarfs, sometimes included, are G-type stars like the Sun, although their “dwarf” status is contextual.
Function and Behavior
Red dwarfs burn hydrogen slowly and steadily, granting them extremely long lifespans. White dwarfs no longer produce energy but emit residual heat radiation. Brown dwarfs emit faintly in the infrared due to internal heat. Gravitational stability is maintained either by fusion processes (red dwarfs) or quantum degeneracy pressure (white and brown dwarfs).
Evolution
A star may become a white dwarf at the end of its life if its initial mass is moderate. Red dwarfs evolve very slowly and have not yet reached final observable stages in the current universe. Brown dwarfs do not undergo significant stellar evolution but cool slowly. The life cycle of a dwarf star depends on its initial mass and internal support mechanisms.
Limits and Distinctions
The term “dwarf star” is not uniform and encompasses diverse objects. It does not indicate a single class but a functional category based on mass, brightness, and evolutionary behavior. Some stars may change classification during their lives. The boundary between massive planet, brown dwarf, and star can be unclear, especially for substellar objects.