Stellar Lifecycle
Every star is born in a molecular cloud and dies according to its mass. The Hertzsprung-Russell diagram plots luminosity against temperature, revealing the main sequence where stars spend most of their lives. Adjust the initial mass and watch the evolutionary track trace across the diagram.
L ∝ M3.5 • Main sequence lifetime ∝ M−2.5
Stellar evolution
A star's life is determined almost entirely by its initial mass. Low-mass stars (< 0.5 M⊙) burn so slowly they outlive the current age of the universe. Solar-mass stars evolve through a red giant phase before shedding their outer layers as a planetary nebula, leaving a white dwarf. Massive stars (> 8 M⊙) end in supernovae, producing neutron stars or black holes.
- Molecular cloud: Gravity collapses a dense region of gas and dust.
- Main sequence: Hydrogen fuses to helium in the core. The star is in hydrostatic equilibrium.
- Red giant: Core hydrogen exhausted. Shell burning causes the envelope to expand and cool.
- White dwarf: The remnant core of a low/intermediate-mass star. Electron degeneracy pressure supports it.
- Neutron star: A collapsed core supported by neutron degeneracy pressure. Mass > 1.4 M⊙ (Chandrasekhar limit).
- Black hole: If the remnant exceeds ~3 M⊙ (TOV limit), nothing stops the collapse.