M2 Stellar Evolution and HR Diagrams

Topic

The central figure of this model is the star throughout its lifetime, represented on a diagram that plots luminosity against temperature.

The main sequence is the diagonal band on that diagram where stars fuse hydrogen in their cores; within this band, the more massive a star is, the hotter and more luminous it appears.

The relationship between a star's mass and its luminosity is so pronounced that a star fifty times more massive than the Sun can be up to a million times more luminous; however, that same disproportionate mass means the star's lifespan on the main sequence is ten thousand times shorter than the Sun's.

Upon exhausting the hydrogen in its core, the star expands toward the giant branch—or, in the most massive cases, toward the supergiant branch; the Sun itself will follow this same path in several billion years.

Isochrones are curves on this diagram that group together stars of the same age but different masses; they serve as a tool for dating an entire star cluster by identifying the precise point where its stellar population diverges from the main sequence.

The final remnant left by each star is entirely determined by its initial mass, following the previously described thresholds of quantum degeneracy: a white dwarf, a neutron star, or a black hole, depending on which threshold was crossed. Thus, from the star's life cycle—with which this document began—to the final remnant with which it concludes, and encompassing the main sequence, the mass-luminosity relationship, and isochrones, stellar evolution dictates that a star's birth mass determines—from start to finish—both the path it traces across the luminosity-temperature diagram and the final form it takes at the end of its life.

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