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Planets Elsewhere?

Planets Elsewhere?. Protoplanetary Disks and universality suggest many stars have planets First discovery in 1988 . Now 853 around 672 stars Finding planets is tough: dim, small, near bright star. 32 planets in 28 systems detected by imaging. Who Orbits Whom?.

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Planets Elsewhere?

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  1. Planets Elsewhere? • Protoplanetary Disks and universality suggest many stars have planets • First discovery in 1988. Now 853 around 672 stars • Finding planets is tough: dim, small, near bright star. 32 planets in 28 systems detected by imaging

  2. Who Orbits Whom? • Planet and Star orbit common center of mass • One detection by Astrometry

  3. How Fast? • 498 planet in 386 systems detected by radial velocity measurements

  4. Transiting Planets • If planet eclipses star can observe light curve • Shape of curve helps find size, mass, even properties of atmosphere of planet • 290 planets in 235 systems detected via transit • Keplerhas 2321 candidate planets in 1290 systems

  5. Other Methods • Gravitational lensing of starlight by planet. 16 planets in 15 systems • Transit Timing Variation uses discrepancies in transit times of eclipsing planet to predict others in same system

  6. What Have We Found? • 1-40% of (Sunlike) stars have planets. Planets are ubiquitous! • Our methods are most sensitive to hot Jupitersso these are mostly what we find • Migration is common as are strongly interacting orbits

  7. What Are They Like? • Taking selection bias into account, super Earths outnumber Jupiters • Some SuperJupiters • Kepler-16b orbits two stars

  8. The Sun Shines – but How? • Sun is big and hot so luminous • How does it stay hot? • Chemical (rearrange electrons - electromagnetic) burning produces per atom, or per kg. • Need to burn so run out in • Kelvin-Helmholtz (gravitational) energy would last

  9. Nuclear Physics • Why don’t nuclei break up under electric repulsion? • A strong attractive force binds nucleons • Short-range since atoms do not collapse

  10. Nuclear Energy • Rearranging nucleons recover nuclear energy • In large nuclei distant nucleons barely attract • Breaking up – fission – or emission recover electromagnetic energy • Heats planets powers reactors

  11. Fusion? • In small nuclei, less attractive interactions • Liberate nuclear energy by fusion to Helium • Problem: Hydrogen is all protons • Strong interactions cannot change a proton to a neutron

  12. Weak Interactions • Something can do this! • And the inverse • A free neutron decays in 15min • Weak nuclear force mediates this decay

  13. Some Questions and Answers • Can a force change one particle into another? • Is a neutron just a tiny Hydrogen atom? • What is ? • Are there any rules? • Conservation Laws • Mass-Energy • Momentum • Angular Momentum • Electric Charge • Electron Number • Weak interaction: rare Yes No

  14. Particle Physics • Antiparticle: same mass opposite charges • Neutrinos almost massless, weakly interacting • Discovered as missing energy in decay

  15. Solar Energy • p-pchain is source of Solar Energy • Sun could last

  16. What it Takes • To initiate fusion, protons must overcome electric repulsion • One proton must inverse decay before highly unstable breaks up • Requires temperatures of - only in core • Inefficient because weak process required

  17. How Do We Know? • Theory (Eddington, Bethe 1932) first • Davis,Bahcall(1968): Detect the • Pro: Penetrate Sun • Con: Penetrate detector • Flux at Earth: • Put a tank with of Chlorine in Homestake Gold Mine • Requires high-energy produced in other processes • Expect one atom per six days

  18. Where Are the Neutrinos? • Flux Found is less than predictions • Is Solar Model wrong? • Is detector model wrong? • Decided in 2001 by SNO: particle physics

  19. More Particles, More Charges

  20. So What? • Neutrinos change spontaneously en route • pp process produces • When they arrive, 1/3 are • This implies, in particular, that neutrinos are not masslessalthough light.

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