An HR Diagram of PMS stars with different masses. The Hayashi Track is depicted as vertical lines, while the Henyey are horizontal. Higher mass stars spend very little time on the Hayashi Track, while the lowest mass stars never reach the Heyney Track, with a gradient seen of time spent on each track as the mass increases.[ 1]
The Henyey track is a path taken by pre-main-sequence stars with masses greater than 0.5 solar masses in the Hertzsprung–Russell diagram after the end of the Hayashi track . The astronomer Louis G. Henyey and his colleagues in the 1950s showed that the pre-main-sequence star can remain in radiative equilibrium throughout some period of its contraction to the main sequence.
The Henyey track is characterized by a slow collapse in near hydrostatic equilibrium , approaching the main sequence almost horizontally in the Hertzsprung–Russell diagram (i.e. the luminosity remains almost constant).[ 2]