Supernova Overview

• Giant stars detonating create cosmic explosions called supernovas
• Dramatic end to massive star's life
• Only biggest stars go supernova (minimum 8x Sun's mass)
• Happening somewhere in universe right now

Betelgeuse Example

• 10th brightest star in night sky
• Red supergiant ~15x Sun's mass
• Size: would stretch to Jupiter's orbit if placed in solar system
• Age: <10 million years old but ready to explode
• When explodes: sky region brightens for 14 days, nearly bright as full moon
• Could happen any moment

Stellar Life Cycle - Energy vs Gravity Battle

• Star's life = constant battle between gravity (inward) and energy (outward)
• Nuclear fusion in core creates outward pressure
• Atoms ram together, stick, form larger atoms
• Giant star fuses 7.5 billion tons hydrogen/second
• Energy equivalent: ~100 billion atomic bombs/second
• Gravity holds explosive energy together
• More massive star = stronger gravity = harder outward push needed

Fusion Sequence Timeline

• 90% of life: hydrogen → helium fusion
• Hydrogen depletion triggers countdown to death
• Helium → carbon fusion: ~1 million years
• Carbon → neon fusion: ~1,000 years
• Neon → silicon fusion: ~1 year
• Silicon → iron fusion: 1 day
• Process accelerates dramatically at each stage

Final Death Throes

• Iron production marks point of no return
• Dense iron sphere forms in core (several thousand miles across)
• Core temperature: ~1 billion degrees
• Iron fusion consumes energy instead of producing it
• Star steals own energy to continue iron fusion
• Growing iron core sucks more energy from star

Core Collapse and Explosion

• Gravity overwhelms outward pressure
• No nuclear reactions left to support star
• Iron core edges collapse
• Trillions of tons dense iron fall inward at 1/4 light speed
• Star has <1 second left to live
• Outer layers don't react immediately (like Wile E. Coyote effect)
• Trillion trillion trillion tons gas rush inward following iron core
• Sets off most dramatic explosion in universe
• Can outshine entire galaxy

Scientific Mystery

• Still don't fully understand how collapsing iron ball + falling gas create giant fireball
• Mechanism of core collapse triggering massive explosion remains partially unexplained