Star Forge

The dial sets the birth mass M, and everything else follows from the chapter’s model: luminosity L = M³·⁵ (in solar units), a surface temperature that rises with mass along the main sequence, and a fuel clock t ∝ M/L = M⁻²·⁵ — which is why a 20 M☉ star lives about ten million years while a 0.5 M☉ dwarf would outlast the current age of the universe more than four times over.

The endpoints are the real thresholds of stellar evolution, simplified to two lines: below about 8 M☉ the collapse of the dead core stops at electron degeneracy — a white dwarf; between 8 and 20 the supernova leaves a neutron star; above 20 nothing stops the fall and a black hole forms. The track the dot follows is the star’s path across the Hertzsprung–Russell diagram: along the main sequence band, up and right to the giant branch, then to whichever corpse the mass decreed.

The twist levels are honest physics too. Demanding a minimum lifetime pushes you to the light end of the allowed window because heavy stars burn fast; outliving a rival means undercutting their mass, since t ∝ M⁻²·⁵ is strictly decreasing. Real astrophysicists play this exact game in reverse: from a cluster’s HR diagram they read which masses have already died, and that dates the cluster.