Ch 26.2 & 3 Life Cycle of Average & Low Mass Stars 1.What are the stages of star low and average mass stars? 2.How does the star’s composition change as it ages (Think fusion)? 3.How does the star’s size, density, brightness, and temperature change as it ages?

Stars form from clouds of dust & gas. Gravity pulls nebula into a core. Temps increase to millions of degrees NUCLEAR FUSION begins! A star is born!

Brighter & hotter Lasts for 10 billion years Small, cool, dim Lasts 100 billion years (fuses slowly)

Expanded Bright (big) Cool Unstable (core contracting while shell expands) Helium fusion in core; Hydrogen fusion in outer layers Our sun would take up the orbits of Venus … maybe Earth

When RED GIANT has iron in core  fusion stops & the star collapses Planetary Nebula = ring of gas cast off by outer layer of Red Giant before collapsing. WHITE DWARFS Small Dense Dim Hot Dying Dim because no real fusion going on. Hot due to residual heat (Why embers of a fire are hot after fire is put out).

No more Fusion Dead Star Dense Dark Cold Not really a Black Dwarf Without fusion, there is no thermal pressure pushing out. Gravity pulls the star into its own center – collapsing it to an Earth-sized core.

Ch 26.3 Check Up 1. How is a protostar different from an actual star? 2.What element is being fused in the core of young stars? Red Giants? 3.How is a star’s mass related to the length of its life cycle? Give an example 4.What are 3 possible end stages for stars (depending on mass)? 5.Which choice best compares a blue star to a yellow star on the main sequence? a.Blue stars are cooler and last longer than yellow stars. b.Blue stars are hotter and last longer than yellow stars. c.Blue stars are cooler and “live” shorter lives. d.Blue stars are hotter and live longer lives.