ISP Chapter 16 - Chapter 16 Dark matter Dark energy the...

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Chapter 16 Dark matter, Dark energy & the fate of the universe What do we mean by dark matter and dark energy? Dark matter : a form of mass that emits little or no light but whose existence we infer from its gravitational influence Dark Energy : An unknown form of energy that seems to be the source of a repulsive force causing the expansion of the universe to accelerate Baryon Normal matter 3 quarks/particle Examples protons, neutrons Everything in this room is baryons (normal matter) what makes us and stars Mass energy contents of the Universe 4.4% baryons o Stars-.6% o Gas-2.8% Dark matter 25% Dark energy 71% What is the evidence for dark matter in galaxies? Method 1 Sun, orbited by planets Stars in binary systems Stars and gas orbiting the centers of galaxies Mass = v 2 r/G Rotation curve: a plot of orbital velocity versus orbital radius Solar system’s rotation curved declines because Sun has almost all the mass WE measure the mass of the solar system using orbits of planets Orbit period Average orbit size Rotation curve of Milky Way stays flat with distance Therefore its mass must be more spread out than in solar system Mass in Milky Way is spread out over a larger region than the stars.
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