Astronomy 100 Exploring the Universe Tuesday, Wednesday, Thursday Tom Burbine [email protected] SunSun videoSolar ConstantSlide Number 5Slide Number 6Slide Number 7Energy Source for SunSlide Number 9Slide Number 10Slide Number 11How does Fusion Convert Mass to EnergyE = mc2LawSlide Number 15ReactionAntiparticlesFusion reactionSlide Number 19Slide Number 20Proton-Proton Chain ReactionNeutrinosHow was the Homestake Gold Mine used to detect neutrinos?What was the solar neutrino problem?Solution of ProblemFusionWhat is happening to the amount of Helium in the Sun?What is happening to the amount of Helium in the Sun?So how does the Sun stay relatively constant in Luminosity (power output)Slide Number 30Slide Number 31Slide Number 32Slide Number 33Parts of Sun CoreSlide Number 35Radiation zoneSlide Number 37Photons emitted from Fusion reactionsSlide Number 39Convection ZoneSlide Number 41Slide Number 42Slide Number 43Slide Number 44Slide Number 45Slide Number 46Slide Number 47Any Questions?Astronomy 100Exploring the UniverseTuesday, Wednesday, ThursdayTom [email protected]• Brightest star in the sky• Closest star to Earth•Next Closest is Alpha Centauri, which is 4.3 light years awaySun video• http://www.space.com/common/media/video/player.php?videoRef=sun_stormSolar Constant• Energy received at Earth’s distance from the Sun• ~1400 W/m2• 50-70 % reaches Earth’s surface• 30% absorbed by atmosphere• 0-20% reflected away by cloudshttp://en.wikipedia.org/wiki/File:Sun_Life.pngAbsorption linesEnergy Source for Sun• Fusing hydrogen into helium– Hydrogen nucleus – 1 proton– Helium nucleus – 2 protons, 2 neutrons• Need high temperatures for this to occur• ~10 to 14 million degrees Kelvinhttp://www.astronomynotes.com/starsun/s3.htmhttp://www.astronomynotes.com/starsun/s3.htmHow does Fusion Convert Mass to Energy• What is the most famous formula in the world?E = mc2• m is mass in kilograms• c is speed of light in meters/s• E (energy) is in joules• very small amounts of mass may be converted into a very large amount of energyLaw• Law of Conservation of mass and energy– Sum of all mass and energy (converted into the same units) must always remain constant during any physical processhttp://observe.arc.nasa.gov/nasa/exhibits/stars/star_6.html1 kg0.993 kg1 kg0.993 kg0.007 kgReaction• 4 protons → helium-4 + 2 neutrinos + energyNeutrino-virtually massless, chargeless particlesPositron-positively charged electron – annihilated immediately by colliding with an electronto produce energyAntiparticles• Antiparticle – particle with the same mass and opposite electric charge• Antiparticles make up antimatter• Annihilation – when a particle and an antiparticle collide•Antimatter is said to be the most costly substance in existence, with an estimated cost of $62.5 trillion per milligram.Fusion reaction• Much more complicated than4 protons → helium-4 + 2 neutrinos + energyDeuteron – Deuterium (hydrogen with a neutron)nucleusProton-Proton Chain Reaction• This reaction occurs ~1038times each second• It if occurred faster, Sun would run out of fuelNeutrinos• Neutrinos – almost massless particles• No charge• It takes a neutrino about 2 seconds to exit the Sun• The neutrino was first postulated in 1930 by Wolfgang Pauli to preserve conservation of energy, conservation of momentum, and conservation of angular momentum during the decay of a neutron into a proton where an electron is emitted (and an antineutrino).• Pauli theorized that an undetected particle was carrying away the observed difference between the energy, momentum, and angular momentum of the initial and final particles.•http://www.scientificamerican.com/podcast/episode.cfm?id=neutrino-mass-upper-limit-estimated-10-06-23How was the Homestake Gold Mine used to detect neutrinos?• A 400,000 liter vat of chlorine-containing cleaning fluid was placed in the Homestake gold mine• Every so often Chlorine would capture a neutrino and turn into radioactive argon• Modelers predict 1 reaction per day• Experiments found 1 reaction every 3 days•Newer detectors used water to look for reactionsWhat was the solar neutrino problem?• Less neutrinos appeared to have been produced from the Sun than expected from modelsSolution of Problem• Neutrinos come in three types (slightly different masses)– Electron neutrino– Muon neutrino– Tau Neutrino• Experiment could only detect electron neutrinos• Fusion reactions in Sun only produced electron neutrinos• Electron neutrinos could change into other types of neutrinos that could not be detected• Neutrino oscillations – one type of neutrino could change into another typeFusion• The rate of nuclear fusion is a function of temperature• Hotter temperature – higher fusion rate• Lower temperature – lower fusion rate• If the Sun gets hotter or colder, it may not be good for life on EarthWhat is happening to the amount of Helium in the Sun?• A) Its increasing• B) its decreasing• C) Its staying the sameWhat is happening to the amount of Helium in the Sun?• A) Its increasing• B) its decreasing• C) Its staying the sameSo how does the Sun stay relatively constant in Luminosity (power output)http://www-ssg.sr.unh.edu/406/Review/rev8.htmlFigure 15.8Figure 15.4Temperature DensityParts of SunCore• Core – 15 million Kelvin – where fusion occursFigure 15.4Radiation zone• Radiation zone – region where energy is transported primarily by radiative diffusion•Radiative diffusion is the slow, outward migration of photonsFigure 15.13Photons emitted from Fusion reactions• Photons are originally gamma rays• Tend to lose energy as they bounce around• Photons emitted by surface tend to be visible photons• Takes about a million years for the energy produced by fusion to reach the surfaceFigure 15.4Convection Zone• Temperature is about 2 million Kelvin• Photons tend to be absorbed by the solar plasma• Plasma is a gas of ions and electrons• Hotter plasma tends to rise• Cooler plasma tends to sinkFigure 15.14Granulation – bubbling pattern due to convectionbright – hot gas, dark – cool gasFigure 15.14Figure 15.10Figure 15.4http://www.hulu.com/watch/81732/3d-sunAny