An Etymological Dictionary of Astronomy and Astrophysics

A period in the → pre-main sequence evolution of a low mass star during which the star has negligible nuclear energy production and low internal temperature. Hence energy transport inside the star takes place dominantly through → convection. The star contracts homologously and evolves in the → H-R diagram along the → hayashi track with decreasing → luminosity and nearly constant → effective temperature. The time
taken by a star of mass M to contract to radius R along a Hayashi track is of the order of the → Kelvin-Helmholtz time: t_KH = 10⁷(M/M_sun)²/(R/R_sun)³ yr.

See also: → Hayashi track; → phase.