The life cycle of stars from birth to death Stellar Evolution The life cycle of stars from birth to death

Nebula condense by accretion Event (shock wave, super nova, etc) triggers nebula collapse

->fusion -> a star Gas & dust attracts due to gravity Contracting matter causes a spinning & flattening Large clump in center = forming star Flat accretion disc = planets When fusion begins, stellar wind pushes out un-clumped matter and gravitational collapse stops nebula Protostar and disc Gravity & heat ->fusion -> a star

Protostar =forming star; not yet fusing “glows” from pressure/friction temperatures (not “shining”)

Thermonuclear Fusion Enough heat & gravity = atoms smashed into each other Universe~80% Hydrogen (H) + 20% Helium (He) + Dust H + H He + light & heat (Star shines!) Neutrino—nearly massless particle with no charge Positron- opposite of an electron; positively charged.

Brown Dwarf? = a failed star; never started fusion Not enough mass in nebula to create enough gravity, pressure and temperature to start fusion <0.075 Solar mass Brown Dwarf

Main Sequence Star = a fusing “adult” star in equilibrium balance Gravity pulling in -makes star smaller Fusion pushing out –makes star bigger Star size = balance point between gravity & fusion Fusion Balloon & N2(l) Demo

Day 2

Fusion “burning” of atoms Hydrogen fuel runs out less pressure to hold up gravity Gravity collapses star heats star fusing bigger atoms Fusion of Helium into Carbon  greater gas pressure  Star expands to new, bigger equilibrium size

Fusing bigger and bigger atoms As each atom runs out the next large atom can be fused But requires more gravity to push together And releases more energy— expands bigger and brighter

Main sequence lifespan-all about mass! Size of nebula determines potential size of main sequence star Big = blue, hot, bright use fuel quickly; short lives Millions of years Small= red, cool, dim Use fuel slowly; long lives Billions-Trillions of years Our sun = G class main sequence Oh Be a Fine Guy/Gal Kiss Me…the reason for the somewhat random letters for star class is because they are the left over letters from a previous classification system. Some letters were dropped and merged and these are the remnants of that first draft system. Two new classes have been added on the lower end. T and Y? For very cool stars (almost brown dwarfs) Main Sequence Stars O B A F G K M

Life stages…it’s all about mass! Our Sun Small Mass Big Mass Biggest Mass

Red Giants-the death throws = Old age star, fusing larger elements Fusion of larger element more powerful -brighter Expanded star cools

Our sun’s expansion --beyond Earth’s orbit?

The End for Small Stars (<8 solar mass) :White Dwarf & Planetary Nebula Pulsing expansion from Red Giant pushes off outer layers to form a ring cloud =Planetary Nebula Not enough gravity to fuse bigger atoms-fusion stops Core contracts to Earth size with no fusion to hold up gravity Core remains very hot, dim =White Dwarf Slowly radiates heat until cold = Black Dwarf The Ring Nebula

Black Dwarf= dead core of small mass star; completely cooled (theoretical) White Dwarf=dead core of a small mass star; still hot but not fusing

Day 3

Big Mass stars….make Super Red Giants

Supernova= collapse & explosion of big mass stars massive gravity fuses bigger elements up to iron (Fe) Iron absorbs heat & cools star Rapid cooling collapses the core Collapsed core creates a shockwave –colliding atoms creates all elements bigger than iron (Fe)

All elements beyond H from stars #1 Made in Big Bang #2-26 Made by fusion in stars All others Made in Supernova

Big Stars end as…Neutron Stars (9-20 solar masses) No more fusion to hold up gravity Gravity strong enough to collapse dead core until atoms crushed to neutrons Extremely dense- size of a city

Most massive stars die as a Black hole No fusion to hold up gravity Gravity so strong that all mass crushed into itself down to a point Gravity so strong not even light can escape

HR Diagram-plots star temp vs brightness

HR Diagram -plots star temp vs brightness

Planet & Sun Size Comparison