Why three numbers (0.08, 8, 25 M☉)?

~0.08 M☉ separates brown dwarfs from hydrogen-burning stars. ~8 M☉ is a rough lower bound for iron-core collapse supernovae in many textbooks. ~25 M☉ is a cartoon split between neutron star and black hole remnants; real models depend on winds, rotation, and binary interaction.

Where is the asymptotic giant branch?

Merged into “red giant” for clarity; intermediate-mass stars have an AGB phase before the planetary nebula.

Stellar Life Cycle

Cloud → MS → giant/SN → WD / NS / BH vs initial mass (schematic).

About this model

This page shows a qualitative branching diagram for single-star evolution as a function of initial mass: collapse from a molecular cloud, protostar phase, main-sequence core hydrogen burning, then post-main-sequence evolution. Below the hydrogen-burning minimum mass (~0.08 M☉), objects become brown dwarfs. Stars up to roughly 8 M☉ typically eject envelopes and leave white dwarfs. More massive stars may explode as core-collapse supernovae, leaving neutron stars or black holes depending on core mass, mass loss, and metallicity — thresholds here are pedagogical, not precise models.

Who it's for: Introductory astrophysics; complements the HR diagram and nuclear binding pages.

Key terms

main sequence
planetary nebula
white dwarf
supernova
neutron star
black hole

How it works

Stellar evolution depends primarily on initial mass. A molecular cloud collapses into a protostar, then settles on the main sequence while fusing hydrogen in the core. After central hydrogen is exhausted, low- and intermediate-mass stars expand along the giant branch, shed envelopes as planetary nebulae, and leave white dwarfs. Above roughly 8 M☉, a star can end in a core-collapse supernova; the compact remnant may be a neutron star or, for the most massive cores, a black hole. Thresholds are schematic — metallicity, rotation, and binary interaction change the story. Low- and intermediate-mass stars (≲8 M☉) shed their envelopes and leave a white dwarf — the Chandrasekhar mass (~1.4 M☉) caps the core.

Key equations

M_min(H burning) ~ 0.08 M☉ (brown dwarf below)

SN core-collapse: typical lower bound ~ 8 M☉ (uncertain)

Frequently asked questions

Why three numbers (0.08, 8, 25 M☉)?: ~0.08 M☉ separates brown dwarfs from hydrogen-burning stars. ~8 M☉ is a rough lower bound for iron-core collapse supernovae in many textbooks. ~25 M☉ is a cartoon split between neutron star and black hole remnants; real models depend on winds, rotation, and binary interaction.
Where is the asymptotic giant branch?: Merged into “red giant” for clarity; intermediate-mass stars have an AGB phase before the planetary nebula.

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