ISU PHY 102 - Formation/Death of Stars (7 pages)

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Formation/Death of Stars



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Formation/Death of Stars

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Lecture number:
23
Pages:
7
Type:
Lecture Note
School:
Illinois State University
Course:
Phy 102 - Atoms to Galaxies
Edition:
1
Unformatted text preview:

PHY 102 1st Edition Outline of Last Lecture I Big Bang Review II The First Epoch a Temperature not time b Predictions III Standard Model s Cosmic Zoo a Quarks b Radiation IV The Second Epoch V The Third Epoch VI The Fourth Epoch VII The Fifth Epoch VIII Proton Proton Reaction IX The Sixth Epoch X The Seventh Epoch XI Summary Outline of Current Lecture I Cosmic Structure Formation II Star Formation III Wrinkles In Spacetime These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute IV Problems with the Standard form of Cosmology V Inflationary Cosmology VI Galaxy Formation Uncertainty VII Death of a Star a White Dwarfs b Black HOles Current Lecture I Cosmic Structure Formation a Today we have a matter dominated universe ruled by the force of gravity i The formation of stars and the organization of stars in clusters raise questions about the formation of the universe ii Some variations need to be accounted for b Slight variations in density produce formation regions for stars and galaxies c 1st generation stars and galaxies have 74 H and 26 He by mass i Oldest stars we see are in globular clusters and tend to have mostly hydrogen and helium and hardly anything else ii E mc2 is the energy poured out from the reactions that produce visible light d 2nd generation stars are enriched our sun is at least a second generation star e Triple Alpha Process i Helium in a core then all the helium in the core is converted to carbon in a matter of minutes II Star Formation a As H and He accrete gas pressure increases limiting further growth unless there is suffiecient matter maximum star mass is about 60Msun b The Jeans mass 105Msun constitutes the minimum amount of mass required for star formation corresponds to globular star cluster c Collapses of smaller clouds are helped along by i Stochastic processes wakes of exploding stars or two or more gas clouds merging ii Compression by magnetic field of galaxy 1 Pushes a gas cloud over its limit and forces stars to be formed iii Spiral galaxies show star formation 1 There are not more stars in the arms of a spiral galaxy but the stars in the brighter regions are younger stars that are massive and bright 2 Large bright stars die out quickly and the magnetic waves in the galaxy III Wrinkles in Spacetime a COBE observed the cosmic microwave background but there was an ever soslight variation in temperature and thus density from point to point across the sky i There is variation in the background radiation we are not quite sure why ii Some areas are hotter some are cooler IV Problems with the Standard Model of Cosmology a The model of the expanding universe works quite well to explain i Olber s paradox 1 The night sky is dark because the universe is expanding proportionally to the light reaching the earth 2 Objects close to the edge of the universe are so red shifted that we no longer see them 3 Cosmological Constant added by Einstein ii X Y and Z abundances 74 26 0 and later iii Hubble s relationship v HR iv 2 725K cosmic background radiation b 3 major problems remain i The flatness problem 1 If shortly after the Big Bang the universe was even remotely nonflat we would not have the relatively flat universe we observe today 2 Why did the universe s original flatness balance on a knife s edge when so many other possibilities existed a 11 dimensions currently known of ii The horizon problem 1 The cosmic microwave background is amazingly uniform but for every minute variations equal to about 00001 K 2 How is this possible when opposite ends of the universe cannot communicate a It appears that multiple universes exist iii The structure problem 1 Friedmann s assumption of homogeneity and isotropy is not entirely correct as seen in the pockets of higher density in the universe as shown in the cosmic background radiation V Inflationary Cosmology a In an attempt to solve these three problems the suggestion was made of an inflationary period in the early universe b Between 10 34 and 10 32 seconds after the Big Bang the universe grew exponentially from the size of a nucleon VI Galaxy Formation Uncertain a Did galaxy or star formation come first i Could be at the same time ii Could be that the gas clouds formed first b Unclear and problem is confounded by the presence of dark matter the nature of which is completely unknown i If it really is law that the period is related to the average distance then the farther out in the galaxy you go the rate of particle s motion should drop of ii This is not the case the velocity of stars remains relatively constant c Its presence is deduced from rotation curves VII Death of a Star a Stars with diferent masses will evolve at diferent rates b H He C N O i All stars begin this way 90 H and 10 He by particle ii As higher pressure and temperatures occur they can collapse into more dense particles c Near the end of their life spans stars become red giants d 3 possible end states determined by the mass of the star i White dwarf low mass 1 Produced in planetary nebula phase where atmosphere begins a runaway process 2 An earth sized core is revealed at 100 000 K a Core becomes larger and hotter as it compresses b The outer envelope of the star expands c Surface layer are charged particles expanding quickly d The larger the star the lower the escape velocity of the outer particles e Outer envelope goes out into space 3 Hotter inner layers take of into space ii Neutron star medium 1 Produced during a supernova explosion resulting in a pulsar 2 Protons and electrons are crushed to produce neutrons a Energy that has been supporting the star is now sucked into the core b Core begins collapsing and a violent explosion occurs c Gas layers surrounding the core iii Black hole high mass 1 Produced in supernova explosions but neutron degeneracy cannot stop collapse neutrons crash into neutrons 2 No known forces can stop the matter from simply vanishing 3 Gravity is so strong that even light cannot escape a Photons become infinitely red shifted and light cannot get out b Physical velocity is greater than the speed of light 4 We know about electromagnetism gravitation strong and weak force 5 Accretion disk such as Cygnus X 1 often found in binary star systems 6 Detection a X ray sources b Gravitational efects on binary star companion c Gravitational lensing i Enough mass that can actually distort the light paths that are coming from far away galaxies d


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