The Lives of Stars

1. The Lives of Stars

2. Copy Evolution of Stars • Newton’s Laws of Gravitation state: • All masses attract each other • This force gets stronger the closer the objects are together • Gravity is constantly at work • It is the force that helps create and build stars, but ultimately causes them to die

3. Copy Nebulae • Astronomers speculate that stars form from gas and dust clouds called nebulae • Gravity pulls the material togethe • Accumulating gas increases temperature • At 10,000,000 degrees nuclear fusion begins (transformation of hydrogen into helium)

4. Copy Main Sequence Stars • Fusion begins • Starts to consume hydrogen • Helium begins to accumulate in the core • Interior begins to heat up increasing temperature and pressure • Forces are balanced by gravitational pull • The time a star takes remains stable depends on mass

5. Copy Low Mass Star (Red Dwarf) • Consume Hydrogen slowly ~100 billion yrs • Lose mass becoming a white dwarf

6. Copy Intermediate Mass Stars(like sun) • Consume Hydrogen faster over about 10 billion yrs • When Hydrogen used up core begins to collapse • Temperature increases • Outer layer begins to expand 10 – 100 times its size • Outer layer is cooler so it looks red (Red Giant) • Sun will eventually become this reaching Mars

7. Copy Intermediate Mass Stars(like sun) • Stellar winds peel off outer layer revealing inner layer • Planetary Nebula • Eventually disperses and star becomes white dwarf • Over time core cools and they become a black dwarf (dark cinder)

8. Copy Massive Stars • Consume Hydrogen quickly • Core gets so hot Helium fuses into heavier elements • Swells into Supergiant • Burn core in ~7 billion years • Helium burning stage ~ 500,000 yrs • Silicon is transformed into iron in 1 day

9. Copy Supernova • Massive stars • After iron core stage no fusion to counteract gravity • Core collapses • Massive shock wave bursts from the star’s surface (Supernova)

10. Copy Neutron Stars • After supernova two possible fates • If core is 1.4 – 3 Solar masses • Gravity collapses remnants into 10 – 20 km diameter (Neutron Star) • Located because they give off pulsars • Greater than 3 solar masses • Form Black Holes • Objects so compact and dense not even light can escape

11. Copy Formation of Stars • People thought space (inter-stellar medium) was empty • Stellar winds • Planetary nebulae • Supernovas • All fill space with large quantities of gas and dust • All essential for making new stars

12. Copy Formation of the Solar System • The theory of how stars and planets are formed is called the solar nebula theory • Scientists suggest the sun is 5 billion yrs old • 9 planets orbiting around it are 4.6 billion yrs old • Catastrophic Theory • Star collided with sun • Debris scattered formed planets

13. Copy Formation of Solar System • Smallest planets closest to sun were blasted with radiation • Didn’t have enough gravity to hold on to their hot atmospheres • Became rocky inner planet (M,V,E,Ma) • Planets farther out kept their gas • Became the gas giants (J,S,U,N,P) • Throughout history loose rocks and dust pounded planets (evidence in craters on Mercury and the Moon) • Mostly cleared up now except for some debris accumulated around planets

14. Copy Hunt for Extra-Solar Planets • Planets products of star formation so they should be fairly common • There are 100 recorded examples of young stars • There are about a dozen extra-solar planets (planets that orbit stars other than the sun) • A planet 2.5 times the size of Jupiter obits a star near the Big Dipper