Star Lifecycle: Mass-Driven Evolution & HR Diagram (2D)

Main Sequence

Initial Mass

Stellar mass 1.0 M☉

Evolution

Life progress 0%

Playback speed 1.0×

Star State

Age

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Fate

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Surface temp.

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Luminosity

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Radius

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MS lifetime

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How it works

Mass alone decides a star's fate. The engine uses the standard piecewise mass–luminosity relation (L∝M^2.3 below 0.43 M☉, L∝M⁴ up to 2 M☉, L∝M^3.5 up to 55 M☉) and an approximate main-sequence mass–radius relation to fix each star's main-sequence luminosity and radius from its mass, then derives its surface temperature from the Stefan–Boltzmann law:

L / L☉ = (R / R☉)² · (T / T☉)⁴
main-sequence lifetime ≈ 10 Gyr · M⁻²·⁵

Below 8 M☉ the core never gets hot enough to fuse carbon: the star swells into a red giant, puffs off a planetary nebula, and its exposed core cools as a white dwarf — dense, tiny (~Earth-sized) and initially very hot. Above 8 M☉ the core keeps fusing all the way to iron, cannot generate more energy, and collapses in a core-collapse supernova; the ~1.4–3 M☉ collapsed core survives as a neutron star (~10 km, city-sized), while above roughly 25 M☉ even neutron degeneracy pressure fails and the core keeps collapsing into a black hole, which emits no thermal light at all.

The right-hand panel is a real Hertzsprung–Russell diagram (temperature decreasing to the right, luminosity on a log scale): every marker's colour comes from a genuine blackbody colour-temperature approximation, and its position always satisfies the Stefan–Boltzmann relation above — a hot-but-tiny white dwarf and a cool-but-enormous red giant can share the same luminosity for exactly that reason.