2. What does the word “Evolution” mean? Bellwork 11/16: If you borrowed a book, please check it in and put it back in the cabinet  1. Describe the basic steps of Stellar Formation (notes from last time). 2. What does the word “Evolution” mean?

Quick and Friendly Reminder… Consider a Unit 2 Test retake Take a reassessment ticket & sign up for ASR Communicate with me, please 

What’s Coming Up? Today: Review Stellar Formation Stellar Evolution Part 2: Life Cycles of Stars! Lab Monday: Lab Comprehension Quiz—did you understand the lab? Stellar Evolution Part 3: Death & Nucleosynthesis Wednesday: Gravity! Everything we’ve talk about so far…PULLED TOGETHER 

Let’s recap stellar formation

Discuss with your table partner: Based on your reading from the book, match each phase of a human life cycle with each phase of a star’s life cycle. Human Life Cycle Stages Stellar Life Cycle Stages Gamete Fetus Childhood-Young Adult Hood Middle Age Old Age-Death Red Giant/Supergiant Fusion Ignition/Main-sequence Nebula Stellar Remnant Protostar

Stellar evolution Changes in a star’s properties over its “life” Stars exist because of gravity Two opposing forces in a star are Gravity – contracts Thermal nuclear energy – expands

Stages (5 Total) Nebula Birth In dark, cool, interstellar clouds Gravity contracts the cloud Temperature rises

Stages 2. Protostar Gravitational contraction of gaseous cloud continues Hydrogen nuclei fuse Become helium nuclei Process is called hydrogen burning Energy is released Outward pressure increases

WAIT! Do all protostars become stars? Nope! Sometimes a protostar does not have enough mass to start hydrogen fusion These “stars” are known as Brown dwarfs Comparable to Jupiter in size& one millionth the luminosity of the sun

3. Main-sequence stage When outward thermal energy pressure is balanced by gravity pulling inward Hydrogen continues to fuse into Helium Luminosity & Temperature are dependent on this “fuel” 90% of a star's life is in the main-sequence Questions 1 & 3 There are lots of types of Main-sequence stars. Why? What determines where they fall on the H-R Diagram?

Main Sequence Stars—a closer look Question 2 Main Sequence Stars—a closer look We said that all stars are made up of mostly H & He…and yet… There are lots of types of Main-sequence stars…why? More mass = more fuel = more energy is radiated

4. Red giant stage Questions 4-7 Hydrogen burning migrates outward Star's outer envelope expands Surface cools & becomes red Core is collapsing as helium is converted to carbon Eventually all nuclear fuel is used Gravity squeezes the star Unbalanced forces Questions 4-7

5. Burnout or Death OPTIONS: White Dwarf Planetary Nebula Supernova Black Hole Neutron star What determines which of these outcomes will occur? Let’s take a look…

Stellar Evolution Simulation You will begin as 1 of 4 main-sequence type stars You will travel through stations, recording your star’s evolution You will be collecting information on intermediate and ending phases

The Basics: You will want to have your labeled HR-Diagram handy  Choose a “star” out the beaker. Determine which type of star you are based on the data given & your HR Diagram Mass Luminosity Temp. 2. Follow the directions at each table. 3. Make sure to collect information at each station 4. Record your evolutionary pathways on the class data table, please.

You can start out as 1 of 4 stars: Brown Dwarf Red Dwarf Average/Solar-type Blue Supergiant Note: these stars are on the main-sequence…

Class Data—2A: Began As… Evolutionary Pathway… Brown Dwarf Red Dwarf Average (Solar-Type) Blue Supergiant

Class Data—1A: Began As… Evolutionary Pathway… Brown Dwarf Red Dwarf Average (Solar-Type) Blue Supergiant

What do we notice about the class data?

Stellar Remnants

White Dwarf Small (some no larger than Earth) Dense Can be more massive than the Sun Spoonful weighs several tons Atoms take up less space Electrons displaced inwards

Neutron Star Forms from a more massive star Remnant of a supernova Star has more gravity Squeezes itself smaller Remnant of a supernova Gravitational force collapses atoms Electrons combine with protons to produce neutrons VERY Small size

Neutron Star Pea size sample Weighs 100 million tons

Black Hole More dense than a neutron star Intense surface gravity lets no light escape As matter is pulled into it Becomes very hot Emits x-rays Likely candidate is Cygnus X-1, a strong x-ray source