 Stellar Evolution (Birth)  Stage 1 - Hydrogen Gas  Gravity pushes in  Hydrogen gas cloud shrinks due to gravity. Pressure of gases heat up cloud.  Stage 2 - T-Tauri  Cool (DIM) Infrared Star  Fusion begins (18+ million degrees)  Stage 3 - Main Sequence  Gravity force inward equalized by heat pressure outward.  Hydrogen fuses to make helium in most stars (up to iron in massive stars).  NOTE: It is the MASS of a STAR that dictates its PAST, PRESENT, and FUTURE!!  Of the 60 nearest stars to Earth, 40 are too dim to see. High Mass 1 Million yearsMiddle Mass10 Billion YearsLow Mass1 Trillion Years Triple Alpha Process  Stellar Evolution (Death)  Stage 4 - Red Giant  Cool and big  Light Stars - Planetary Nebula Stage  White Dwarf  Small, dense, hot, electron degeneracy  Black Dwarf Stage  Final density, cold dead cinder  Heavy Stars - Supernova Explosion (1 trillion degrees, elements above iron formed)  Neutron Star (Pulsar)  Black Holes  Developing Black Hole  Exit Cone: hypothetical inverted cone.  Light from inside the cone will escape.  Light from outside the cone will fall back and not escape.  Light along edge of cone will neither fall back nor escape.  Creates a "Photon Sphere" of light (9 miles out)  Exit cone continues to shrink to nothing  Then no more light can escape: Fully Developed Black Hole Event Horizon (6 miles out)  Objects reach speed of light.  Galaxy Groups  Local Groups (2 Dozen)  Ours: 2 Large  Milky Way  Andromeda  2 Irregular  Large Magellenic Cloud  Small Magellenic Cloud  Orbit Milky Way 150,000 and 180,000 light years away  Superclusters: 50-100 local groups or more  Ours: Virgo Supercluster  Giant Strings of Superclusters  "Great Wall" (500 million light years)  Intergalactic Space: Region beyond the galaxies  1 Hydrogen atom/cubic centimeter  2 kinds of Hydrogen  Normal Hydrogen (1 proton, 1 electron) H1  Ionized hydrogen (1 proton) H2  Cosmology: Study of structure of the universe  Olbers Paradox: proof that the universe does not extend to infinity.  3 Models of the Universe  Steady State  Universe has always existed  Problem: universe is expanding  No evidence to indicate new mass being formed to fill void as universe expands  Big Bang  Universe is 13-18 billion years old  Ylem: Point of origin  Support  Red Shift  Radio waves left from big bang (COBE)  Oscillating Big Bang  Universe will contract: Big Crunch  Currently not evidence of enough matter  Dark Matter  Matter in the universe that we can't see.  May represent 99% of mass of universe (visible mass only 1%)  Dark Energy  Mysterious energy that provides the force to cause universe to accelerate