Zero age main sequence

Evolutionary tracks

When a main-sequence star has consumed the hydrogen at its core, the loss of energy generation causes its gravitational collapse to resume and the star evolves off the main sequence. The path which the star follows across the HR diagram is called an evolutionary track. A track known as the zero age main sequence (ZAMS) is where stars of different masses begin their main sequence lives, while a track known as the terminal age main sequence (TAMS) is where stars of different masses end their main sequence lives when hydrogen is depleted in their cores.