gen-define-the-life-cycle-of-a-star-and-give-one-short-worked-ex-2986

Define the life cycle of a star and give one short worked example.

# Life Cycle of a Star The life cycle of a star depends on its initial mass: ## Main Sequence Stars (like our Sun) 1. **Nebula** - Cloud of gas and dust collapses under gravity 2. **Protostar** - Material heats up as it compresses 3. **Main Sequence** - Nuclear fusion of hydrogen into helium begins (most of star's life) 4. **Red Giant** - Hydrogen depleted; star expands and cools 5. **Planetary Nebula** - Outer layers expelled 6. **White Dwarf** - Dense core remnant slowly cools ## Massive Stars (>8 solar masses) Follow similar early stages but end as: - **Red Supergiant** → **Supernova** → **Neutron Star** or **Black Hole** --- ## Worked Example: The Sun's Lifetime **Given:** - Sun's mass = 2 × 10³⁰ kg - 10% available for fusion - Mass-energy conversion: E = mc² - Solar luminosity = 4 × 10²⁶ W **Calculate main sequence lifetime:** Energy available = 0.007 × 0.1 × (2 × 10³⁰) × (3 × 10⁸)² = 1.26 × 10⁴⁴ J Lifetime = Energy / Luminosity = 1.26 × 10⁴⁴ / 4 × 10²⁶ = **3.15 × 10¹⁷ seconds ≈ 10 billion years** The Sun is currently ~4.6 billion years old, about halfway through its main sequence life.