The Lives of Stars

Evolution of Stars Newton’s Laws of Gravitation state: 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

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)

Main Sequence Stars Fusion begins Starts to consume hydrogen 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

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

Intermediate Mass Stars(like sun) 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

Intermediate Mass Stars(like sun) 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)

Massive Stars Consume Hydrogen quickly 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

Supernova Massive stars 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)

Neutron Stars After supernova two possible fates 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

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

Formation of the Solar System 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

Formation of Solar System 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

Hunt for Extra-Solar Planets 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