Astronomy 101 The Solar System Tuesday, Thursday Tom Burbine [email protected] 3Exam #2Review SessionHWs #6, #7, #8, and #9Milky Way GalaxySlide 8Life of a StarSlide 10CondensingProtostarSlide 13When does a protostar become a starSlide 15Slide 16Slide 17Brown DwarfsMain SequenceSlide 20Sun ends it time on the main sequenceSlide 22Why does the star expand?And ..And …Slide 26Slide 27WhenSlide 29Helium FlashHoweverAndSlide 33NowSlide 35Slide 36Planetary NebulaeSlide 38White DwarfSlide 40Slide 41Slide 42High-Mass StarsSlide 44Stages of High-Mass Star’s LifeFusion in High-Mass starsSlide 47FusionSlide 49Slide 50Slide 51“Deaths” of StarsWhite DwarfsSlide 54Slide 55Electron Degeneracy PressureSlide 57So What Does This MeanOne Interesting ThingWhite Dwarf LimitThe SunBlack DwarfNeutron StarHow do you make a neutron star?SupernovaSlide 66Slide 67Slide 68Slide 69This stops with IronSlide 71InitiallyThenSlide 74DensityExplosionHow do we know there are neutron stars?PulsarsSlide 79Slide 80Black HolesBlack HoleSlide 83Event HorizonHow do calculate the radius of the Event Horizon?Black Hole SizesSlide 87Can you see a Black Hole?NoEvidenceSlide 91Any Questions?Astronomy 101The Solar SystemTuesday, ThursdayTom [email protected]•Course Website:–http://blogs.umass.edu/astron101-tburbine/•Textbook:–Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny.•You also will need a calculator.•There is an Astronomy Help Desk that is open Monday-Thursday evenings from 7-9 pm in Hasbrouck 205.•There is an open house at the Observatory every Thursday when it’s clear. Students should check the observatory website before going since the times may change as the semester progresses and the telescope may be down for repairs at times. The website is http://www.astro.umass.edu/~orchardhill/index.html.Exam #2•February 25th–Covers from last exam up to Feb. 18•Formulas:•T (K) = T (oC) + 273.15•c = f*•E = h*f•KE = 1/2mv2•E = mc2•Power emitted per unit surface area = σT4•λmax (nm) = (2,900,000 nm*K)/T•Apparent brightness = Luminosity 4 (distance)2Review Session•6 pm in Hasbrouck 20 on Wednesday (Feb. 24)HWs #6, #7, #8, and #9Milky Way Galaxy•Interstellar Medium – matter between stars•Made up of gas and dustLife of a Star•A star-forming cloud is called a molecular cloud because low temperatures allow Hydrogen to form Hydrogen molecules (H2)•Temperatures like 10-50 KRegion is approximately 50 light years acrossCondensing•Molecular clouds tends to be lumpy•These lumps tend to condense into stars•That is why stars tend to be found in clustersProtostar•The dense cloud fragment gets hotter as it contracts•The cloud becomes denser and radiation cannot escape•The thermal pressure and gas temperature start to rise and rise•The dense cloud fragment becomes a protostarWhen does a protostar become a star•When the core temperatures reaches 10 million K, hydrogen fusion can start occurring•Because nuclear reactions have not yet begun in the protostar’s core, this luminosity is due entirely to the release of gravitational energy as the protostar continues to shrink and material from the surrounding fragment•http://www.youtube.com/watch?v=W13ZYepDBvo•http://www.youtube.com/watch?v=QFklLMB_ZOI&feature=relatedBrown Dwarfs•Failed stars•Not enough mass for fusion•Minimum mass of gas need for fusion is 0.08 solar masses (80 times the mass of Jupiter)Main Sequence•Is not an evolutionary track–Stars do not evolve on it•Stars stop on the main sequence and spend most of their lives on itSun ends it time on the main sequence•When the core hydrogen is depleted, nuclear fusion stops•The core pressure can no longer resist the crush of gravity•Core shrinksWhy does the star expand?•The core is made of helium•The surrounding layers are made of hydrogenAnd ..•Gravity shrinks the inert helium core and surrounding shell of hydrogen•The shell of hydrogen becomes hot for fusion•This is called hydrogen-shell burningAnd …•The shell becomes so hot that its fusion rate is higher than the original core•This energy can not be transported fast enough to surface•Thermal pressure builds up and the star expandsAnd ..•More helium is being created•Mass of core increases•Increases its gravitational pull•Increasing the density and pressure of this regionWhen•When helium core reaches 100 million Kelvin,•Helium can fuse into a Carbon nucleusHelium Flash•The rising temperature in the core causes the helium fusion rate to rocket upward•Creates a lot of new energyHowever•The core expands•Which pushes the hydrogen-burning shell outwards•Lowering the hydrogen-burning shell’s temperatureAnd•Less energy is produced•Star starts to contractNow•In the core, Helium can fuse to become Carbon (and some Oxygen)•Star contracts•Helium fusion occurs in a shell surrounding the carbon core•Hydrogen shell can fuse above the Helium shell•Inner regions become hotter•Star expandshttp://upload.wikimedia.org/wikipedia/commons/8/8d/Triple-Alpha_Process.png–Triple Alpha Process–4He + 4He ↔ 8Be–8Be + 4He ↔ 12C + gamma ray + 7.367 MeV•Some carbon fuses with He to form Oxygen•12C + 4He → 16O + gamma ray•Harder to fuse Oxygen with Helium to produce NeonPlanetary Nebulae•There is a carbon core and outer layers are ejected into space•The core is still hot and that ionizes the expanding gasPlanetary NebulaeWhite Dwarf•The remaining core becomes a white dwarf•White dwarfs are usually composed of carbon and oxygen (can not fuse carbon)•Oxygen-neon-magnesium white dwarfs can also form (hot enough to fuse carbon but not neon)•Helium white dwarfs can formHigh-Mass Stars•The importance of high-mass stars is that they make elements heavier than carbon•You need really hot temperatures which only occur with the weight of a very high-mass starStages of High-Mass Star’s Life•Similar to low-mass star’s•Except a high-mass star can continue to fuse elements•When the fusion ceases, the star becomes a supernova•Supernova is a huge explosionFusion in High-Mass stars•Besides fusion of Hydrogen into Helium•The high temperatures allow Carbon, Nitrogen, and Oxygen to be catalysts for converting Hydrogen into HeliumCNO cycleFusion•The interior temperatures of high-mass stars in its late-stage of life can reach temperatures above 600
View Full Document
Unlocking...