Copyright © 2009 Pearson Education, Inc.Chapter 13The Bizarre Stellar GraveyardCopyright © 2009 Pearson Education, Inc.Don McLeroyTexas State Board of EducationWhat is this bigger target? In the words of Phillip Johnson it is“metaphysical naturalism” or “materialism” or just plain old“naturalism”; it is the idea that nature is all there is. Modern sciencetoday is totally based on naturalism. In all of intelligent design'sarguments against both Darwinian evolution, and the chemical originof life, it is their naturalistic base that is the ultimate target. Theimportant aspect of Darwinian evolution is its naturalistic claim thatall life is a result of purposeless, unintelligent, material causes.And why is intelligent design considered a “big tent”? It is becauseanyone opposed to naturalism is welcomed into the movement. Allof us, progressive creationists, recent creationists, old earthers, andyoung earthers are welcomed in this tent. Intelligent design here atGrace Bible Church is a smaller tent than the intelligent designmovement itself. We are all biblical literalists and believe the Bibleto be inerrant. It is good to remember that the intelligent designmovement is a bigger tent. There is no reason to attack one anotherover our disagreements, though we should rigorously examine ourBible, and see how our views fit the Scriptures and how coherent acreation story they tell. Remember, naturalism is the main target.Copyright © 2009 Pearson Education, Inc.13.1 White DwarfsOur goals for learning:• What is a white dwarf?• What can happen to a white dwarf in a closebinary system?Copyright © 2009 Pearson Education, Inc.White Dwarfs• White dwarfs arethe remaining coresof dead stars.• Electrondegeneracy pressuresupports themagainst gravity.Copyright © 2009 Pearson Education, Inc.White dwarfs cool off and grow dimmer with time.Copyright © 2009 Pearson Education, Inc.Size of a White Dwarf• White dwarfs with the same mass as theSun are about the same size as Earth.• Higher-mass white dwarfs are smaller.Copyright © 2009 Pearson Education, Inc.The White Dwarf Limit• Quantum mechanics says that electrons must movefaster as they are squeezed into a very small space.• As a white dwarf’s mass approaches 1.4MSun, itselectrons must move at nearly the speed of light.• Because nothing can move faster than light, a whitedwarf cannot be more massive than 1.4MSun, the whitedwarf limit (also known as the Chandrasekhar limit).Copyright © 2009 Pearson Education, Inc.What can happen to a whitedwarf in a close binary system?Copyright © 2009 Pearson Education, Inc.Nova• The temperature ofaccreted mattereventually becomeshot enough forhydrogen fusion.• Fusion beginssuddenly andexplosively,causing a nova.Copyright © 2009 Pearson Education, Inc.Nova• The nova starsystem temporarilyappears muchbrighter.• The explosiondrives accretedmatter out intospace.Copyright © 2009 Pearson Education, Inc.Thought QuestionWhat happens to a white dwarf when it accretes enoughmatter to reach the 1.4MSun limit?A. It explodes.B. It collapses into a neutron star.C. It gradually begins fusing carbon in its core.Copyright © 2009 Pearson Education, Inc.Thought QuestionWhat happens to a white dwarf when it accretes enoughmatter to reach the 1.4MSun limit?A. It explodes. B. It collapses into a neutron star.C. It gradually begins fusing carbon in its core.Copyright © 2009 Pearson Education, Inc.Two Types of SupernovaMassive star supernova:Iron core of massive star reacheswhite dwarf limit and collapses into aneutron star, causing an explosion.White dwarf supernova:Carbon fusion suddenly begins as whitedwarf in close binary system reaches white dwarf limit, causing a total explosion.Copyright © 2009 Pearson Education, Inc.One way to tell supernova types apart is with a lightcurve showing how luminosity changes with time.Copyright © 2009 Pearson Education, Inc.Supernova Types:Massive Star or White Dwarf?• Light curves differ• Spectra differ (exploding white dwarfsdon’t have hydrogen absorption lines)Copyright © 2009 Pearson Education, Inc.What have we learned?• What is a white dwarf?— A white dwarf is the inert core of a dead star.— Electron degeneracy pressure balances theinward pull of gravity.• What can happen to a white dwarf in aclose binary system?— Matter from its close binary companion canfall onto the white dwarf through anaccretion disk.— Accretion of matter can lead to novae andwhite dwarf supernovae.Copyright © 2009 Pearson Education, Inc.13.2 Neutron StarsOur goals for learning:• What is a neutron star?• How were neutron stars discovered?• What can happen to a neutron star in a closebinary system?Copyright © 2009 Pearson Education, Inc.What is a neutron star?Copyright © 2009 Pearson Education, Inc.A neutron staris the ball ofneutrons leftbehind by amassive-starsupernova.The degeneracypressure ofneutronssupports aneutron staragainst gravity.Copyright © 2009 Pearson Education, Inc.Electron degeneracypressure goes awaybecause electronscombine with protons,making neutrons andneutrinos.Neutrons collapse to thecenter, forming aneutron star.Copyright © 2009 Pearson Education, Inc.A neutron star is about the same size as a small city.Copyright © 2009 Pearson Education, Inc.Discovery of Neutron Stars• Using a radio telescope in 1967, Jocelyn Bellnoticed very regular pulses of radio emissioncoming from a single part of the sky.• The pulses were coming from a spinning neutronstar—a pulsar.Copyright © 2009 Pearson Education, Inc.Pulsar at centerof Crab Nebulapulses 30 timesper secondCopyright © 2009 Pearson Education, Inc.X rays Visible lightCrab Nebula Movie-CHANDRACopyright © 2009 Pearson Education, Inc.PulsarsA pulsar is aneutron star thatbeams radiationalong a magneticaxis that is notaligned with therotation axis.Copyright © 2009 Pearson Education, Inc.PulsarsThe radiationbeams sweepthrough space likelighthouse beams asthe neutron starrotates.Copyright © 2009 Pearson Education, Inc.Neutron Star Limit• Quantum mechanics says that neutrons in thesame place cannot be in the same state.• Neutron degeneracy pressure can no longersupport a neutron star against gravity if its massexceeds about 3MSun.Copyright © 2009 Pearson Education, Inc.What have we learned?• What is a neutron star?— A ball of neutrons left over from a massivestar supernova and supported by neutrondegeneracy pressure• How were neutron stars
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