HAYASHI LIMIT Meaning and
Definition
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Hayashi limit refers to a critical threshold in stellar evolution beyond which a star becomes incapable of igniting and sustaining nuclear fusion in its core. This limit is named after the Japanese astrophysicist Chushiro Hayashi, who first proposed this concept in the 1960s. It represents the minimum mass requirement for stable hydrogen burning in a star's core.
According to the Hayashi limit, stars below a certain mass, called the Hayashi mass, are not massive enough to generate the high pressures and temperatures needed to initiate hydrogen fusion through gravitational collapse. As a result, these low-mass stars, known as brown dwarfs, remain in a state of sub-stellar equilibrium by emitting radiation as they gradually cool and contract over time.
The Hayashi limit is of significant importance in understanding stellar evolution and differentiating between stars and sub-stellar objects. Stars above the Hayashi limit possess sufficient mass and gravitational forces to compress their cores and sustain nuclear fusion, leading to long-lasting energy generation and the emission of visible light and heat as a result. Conversely, objects below the Hayashi limit lack the sustained nuclear reactions required for steady energy production, causing them to be relatively dim and cool.
The Hayashi limit serves as a fundamental boundary that distinguishes the lowest-mass stars from brown dwarfs, thereby helping astronomers classify and comprehend the various celestial objects throughout the universe.
Etymology of HAYASHI LIMIT
The etymology of the term "Hayashi limit" can be traced back to the Japanese astronomer Chushiro Hayashi. Hayashi proposed a theoretical boundary known as the "Hayashi track" in the 1960s, which describes the evolution of young stars on the Hertzsprung-Russell diagram. The Hayashi track represents the path that a collapsing cloud of gas and dust, known as a protostar, follows as it contracts and heats up.
The term "Hayashi limit" is derived from the Hayashi track, but it specifically refers to the boundary where the track ends. The Hayashi limit marks the point at which a protostar has reached a stable state on the main sequence of stellar evolution. It signifies that the protostar has achieved equilibrium between the inward force of gravity and the outward force generated by nuclear fusion in its core.
