Henyey track
Radiative contraction path for pre-main-sequence stars above 0.5 solar masses.
Stars more massive than half the Sun's mass follow the Henyey track on the Hertzsprung-Russell diagram after finishing the Hayashi track. This path involves a slow, nearly hydrostatic collapse, moving almost horizontally toward the main sequence while keeping luminosity fairly steady. In the 1950s, Louis G. Henyey and his team demonstrated that such a pre-main-sequence star can stay in radiative equilibrium during part of its contraction to the main sequence.
Quick Facts
- Mass threshold
- greater than 0.5 solar masses
- Key figure
- Louis G. Henyey
Facts from the source article.
Deviation from Hayashi Track
The transition from the Hayashi track to the Henyey track depends on the star's initial mass. Stars with high opacity are convective, while low opacity leads to radiative heat transfer. Protostars on the Hayashi track are fully convective and optically thick due to H- ions. As the central core contracts and reaches a certain temperature threshold, H- ions break apart, decreasing opacity. For stars massive enough (0.5 solar mass or more), the core becomes sufficiently hot and less opaque, making convection inefficient and the core fully radiative. During this phase, luminosity stays constant or gradually increases while temperature rises as the core undergoes radiative contraction. At the end of the track, nuclear burning begins, causing a dip in luminosity before the star reaches the main sequence. More massive stars evolve quickly from the Hayashi track; less massive stars enter later. Stars below the mass threshold never develop a radiative core and remain on the Hayashi track until the main sequence.
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