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Looking for intelligent life in the Milky Way galaxy • First Any evidence of planets outside of the solar system? Yes! • Second How to detect intelligent life. Radio communication. • Third Probability of locating intelligent life elsewhere. Slide 1 Slide 2 p.416 About 150 planets discovered around other stars. Most are massive and close to the star! Why? vstar α Mplanet/√a The closer the planet the star and the larger the mass, the larger the velocity of the star. That is why most of the discovered planets have a distance of less than 1 AU and mass like Jupiter. Slide 3 p.188 Theory on formation of planets As protostars collapse under gravity the material flattens! Solar system: all major the planets are in one plane! Any evidence besides Solar system? Yes! Slide 4 Fig. 9-5, p.191 Conservation of angular momentum: Mω²r = constant The smaller is r, the faster the angular velocity ω. As stellar system contracts under gravity, it speeds up, which flattens the system. Ultimately the flattened material forms the planets. Slide 5 Fig. 9-3, p.190 Β Pectoris dust ring, Slide 6 Fig. 9-11, p.197 Protoplanetary disks around a star Slide 7 Fig. 9-12a, p.198 An edge-on dust ring blocks light from reflection nebulae around a young solar-type star Slide 8 Fig. 9-14, p.198 a Vstar α Mplanet/√a Slide 9 Detection of planets using Doppler shift Fig. 9-6, p.193 Slide 10 Fig. 9-7, p.194 Discovery of planets using occultation Slide 11 Fig. 9-8a, p.195 We also have one direct evidence of a planet! Slide 12 Fig. 9-8b, p.195 How to detect intelligent life? Radio waves! Arecibo Radio Telescope in Puerto Rico Very Large Array VLA Slide 13 Fig. 20-17, p.428 The message sent to the globular cluster M13 Slide 14 Fig. 20-13, p.424 Probability of Finding Technological Civilizations In the Milky Way Galaxy 1. Number of stars in Milky Way 2. Single stars (0.5) 3. F, G and K stars only. (0.1) Only Sun like stars. 4. Fraction of single stars with planets. (1) 5. Fraction with habitable planets (0.1) 6. Probability to start life. (1) 7. Produce intelligence. (0.1) 8. Communicative intelligence. Radios (0.1) Ants, bees do not communicate. 21011. 11011 . 11010. 11011. 1109. 1109. 1108. 1107. 9. Longevity of the technological society, (10-6) 10 stars •If longevity is 10,000 years out of 11010 years, then fraction is (10-6). •If lifetime is forever once it starts. It took on Earth almost 5 billion years for communicative technology to get started. The Sun will live 10 billion years. 9. Longevity of the technological society, (0.5) 5106 stars. •If 5,000,000 star systems have communicative intelligence, then the probability of the nearest with star with communicative intelligence is 600 light years. Slide 15 Slide 16 Fig. 20-18, p.428