28.3 LIFE CYCLE OF STARS Stage 1 Stage 2 Stage 3

Stage 1 Stage 2 Stage 3 Main Sequence Star (stars like our Sun) Main sequence stage, last the longest Star stays until all H2 fuel is used up (converted to He) He core shrinks and Contracts to produce additional heat. H2 fusion starts in the outer Layers causing the star to swells– moves to next stage. Main Sequence Star (stars like our Sun) less than 8 solar masses Nebula spins & flattens To form a protostar Protostar shrinks due to gravitional attraction. As temperature increases and pressure increases, light and heat are emitted Energy is produced from Nuclear fusion of H2 into He begins – moves to next stage Core temperature increases to a point that He can fuse into heavier elements (O2 and C) H2 into He continues in the outer layers. When Hydrogen is exhausted the outer layers blow away leaving only the carbon-oxygen core – White Dwarf. Expelled layer absorbs the white dwarfs ultraviolet emission causing a halo affect called a Planetary Nebula

Stage 1 Stage 2 Stage 3 Massive Star 8 solar masses or more Same process however due to the more massive size it swells to an even larger size than the main sequence star does Same process however much more dust and gas present Fusion in core continues until iron forms Iron does not release energy so it absorbs it, thus leading to a quick collapse resulting in an explosion – Supernova. Massive star that is 8-15 solar masses, creates a neutron star following the supernova Massive star that is more than 15 Solar masses, creates a black hole following the supernova.

HR Diagram Gives you a picture of the star’s life Luminosity versus temperature Color indicates temperature

HR Diagram Groups Main Sequence Giant Stars 90% of all stars Band across diagram with varying temps (colors) Star is in middle of its life Sun is here Giant Stars Next stage in Sun’s life To the right above main sequence More bright than main sequence because they’re bigger Cooler stars

HR Diagram Groups Red Super Giants 4. Blue Super Giants White Dwarfs Upper right hand corner (above Giant stars) Massive stars at end of life Very cool, but size gives them luminosity 4. Blue Super Giants Very rare, large hot, bright stars at end of life White Dwarfs Lower left corner Hot, dim main sequence stars at end of their life small

Galaxies and the Universe Look like hazy patches- need telescope to view Classified based on shape Spiral (ex. Milky Way—our galaxy) Elliptical are near spherical to lens-shape Irregular (ex. The two Magellanic Clouds

Origin of the Universe Big Bang Theory– explains history/creation of the universe Approximately 10-20 billion years ago all matter in the universe existed in an incredibly hot and dense state, from which it expanded and cooled slowly condensing into stars and galaxies. Evidence is Redshift of cosmic background discovered by Edwin Hubble