Stellar Evolution and Supernovae Summary

Stellar Evolution

  • Solar Mass Star Stages: Protostar, Main-Sequence, Red Giant, Planetary Nebula, White Dwarf.

Star Clusters

  • Types: Globular Clusters (up to 2 million2 \text{ million} stars, diameter ∼100 pc\sim 100 \text{ pc}) and Open Clusters (few hundred stars).
  • Used for age determination via H-R Diagram turn-off points.

Medium-Mass Stars

  • Produce Helium via CNO cycle; red giants ignite Helium smoothly.
  • Final fate: planetary nebula leading to a Carbon/Oxygen white dwarf.
  • Can exhibit variability (e.g., Cepheid variables) due to instability.

High-Mass Stars

  • Evolve quickly, forming elements up to iron in an onion-layer structure.
  • An iron core leads to catastrophic collapse (under electron degeneracy limit) and a supernova explosion.

Supernovae Types

  • Type Ia: White dwarfs beyond 1.4M⊙1.4 M_{\odot} undergo runaway fusion; no remnant; useful as standard candles for distance.
  • Type II: Massive star core collapse; leaves neutron star or black hole; identifiable by hydrogen in spectrum.