Outline

Stellar Evolution 211

7.1 The Evolution of a Star 212

The Sun's Life Story 213

The Life Story of a High-Mass Star 214

The Importance of Gravity 215

7.2 Star Formation 216

Interstellar Gas Clouds 216

Protostars 217

Bipolar Flows from Young Stars 217

Stellar Mass Limits 219

7.3 Main-Sequence Stars 220

Why a Star's Mass Determines Its Core Temperature 220

Structure of High-Mass and Low-Mass Stars 220

Main-Sequence Lifetime of a Star 221

7.4 Giant Stars 222

Leaving the Main Sequence 222

Nuclear Fuels Heavier Than Hydrogen 222

Degeneracy in Low-Mass Stars 223

7.5 Yellow Giants and Pulsating Stars 224

Why Do Stars Pulsate? 224

The Period-Luminosity Law 226

7.6 Death of Stars Like the Sun 226

Ejection of a Low-Mass Star's Outer Layers 226

Re-Modeling: Planetary Nebulas 227

Planetary Nebulas 227

7.7 Old Age of Massive Stars 229

Formation of Heavy Elements: Nucleosynthesis 230

Core Collapse of Massive Stars 230

Supernova Explosions 231

Supernova Remnants 231

7.8 History of Stellar Evolution Theories 233

7.9 Testing Stellar Evolution Theory 234

Extending Our Reach: Measuring the Age of a Star Cluster 235