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Dark Matter Mathematics Janet Moore NASA Educator Ambassador Merry-Go-Round Velocity (v) Velocity vs. Radius Distance (r) Merry-Go-Round Velocity (v) Velocity vs. Radius Distance (r) Solar System Velocity (v) Velocity vs. Radius Distance (r) Solar System Velocity (v) Velocity vs. Radius Distance (r) Solar System Mass (m) Mass vs. Radius Distance (r) Solar System Mass (m) Mass vs. Radius Distance (r) In Summary - Solar System Orbital speed depends on force of gravity Force of gravity depends on mass within the radius Therefore, orbital speed depends on mass within the radius What About Galaxies? How would you expect stars to move around in a spiral galaxy? What would you expect the mass distribution in a spiral galaxy to be? The Activity - NGC 2742 You will be given: Rotation Curve (velocity vs. radius) Luminosity Curve (luminosity vs. radius) Use the Data Chart to analyze the mass in the galaxy G = 4.31 x 10-6 Sample Data Chart Radius Grav. Mass 1.5 e9 Lum. 1 Rot. Vel. 80 3 e8 Lum. Mass 6 e8 Lum/ Grav 0.4 3 100 6.9 e9 1 e9 2 e9 0.29 5 120 1.7 e10 2 e9 4 e9 0.24 8 140 3.6 e10 3.5 e9 7 e9 0.19 Evidence for Dark Matter Light (visible matter) drops off as you go farther out in a galaxy BUT . . . Velocities do not drop off Result: Dark Matter mass is about 10x Luminous Matter mass What is Dark Matter? Baryonic (Normal) Matter: Low mass stars, brown dwarfs (likely), large planets, meteoroids, black holes, neutron stars, white dwarfs, hydrogen snowballs, clouds in halo. Non-Baryonic (Exotic) Matter: Hot Dark Matter: fast-moving at time of galaxy formation, eg massive neutrinos Cold Dark Matter: slow-moving at times of galaxy formation, eg WIMPs -- particle detector experiments looking for them NASA’s Fermi Mission Formerly known as the GLAST mission Launched June 11, 2008 Studying gamma ray sources in the universe Studying potential sources of dark matter in the universe Questions? Janet Moore [email protected] epo.sonoma.edu My Other Workshops: NEWTON’S LAWS11:00 am - Room 207 PI IN THE SKY 3:30 pm - Room 262