Chapter 13 The Bizarre Stellar Graveyard Copyright 2009 Pearson Education Inc Don McLeroy Texas State Board of Education What 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 science today is totally based on naturalism In all of intelligent design s arguments against both Darwinian evolution and the chemical origin of life it is their naturalistic base that is the ultimate target The important aspect of Darwinian evolution is its naturalistic claim that all life is a result of purposeless unintelligent material causes And why is intelligent design considered a big tent It is because anyone opposed to naturalism is welcomed into the movement All of us progressive creationists recent creationists old earthers and young earthers are welcomed in this tent Intelligent design here at Grace Bible Church is a smaller tent than the intelligent design movement itself We are all biblical literalists and believe the Bible to be inerrant It is good to remember that the intelligent design movement is a bigger tent There is no reason to attack one another over our disagreements though we should rigorously examine our Bible and see how our views fit the Scriptures and how coherent a creation story they tell Remember naturalism is the main target Copyright 2009 Pearson Education Inc 13 1 White Dwarfs Our goals for learning What is a white dwarf What can happen to a white dwarf in a close binary system Copyright 2009 Pearson Education Inc White Dwarfs White dwarfs are the remaining cores of dead stars Electron degeneracy pressure supports them against 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 the Sun 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 move faster as they are squeezed into a very small space As a white dwarf s mass approaches 1 4MSun its electrons must move at nearly the speed of light Because nothing can move faster than light a white dwarf cannot be more massive than 1 4MSun the white dwarf limit also known as the Chandrasekhar limit Copyright 2009 Pearson Education Inc What can happen to a white dwarf in a close binary system Copyright 2009 Pearson Education Inc Nova The temperature of accreted matter eventually becomes hot enough for hydrogen fusion Fusion begins suddenly and explosively causing a nova Copyright 2009 Pearson Education Inc Nova The nova star system temporarily appears much brighter The explosion drives accreted matter out into space Copyright 2009 Pearson Education Inc Thought Question What happens to a white dwarf when it accretes enough matter 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 Question What happens to a white dwarf when it accretes enough matter 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 Supernova Massive star supernova Iron core of massive star reaches white dwarf limit and collapses into a neutron star causing an explosion White dwarf supernova Carbon fusion suddenly begins as white dwarf 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 light curve 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 dwarfs don 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 the inward pull of gravity What can happen to a white dwarf in a close binary system Matter from its close binary companion can fall onto the white dwarf through an accretion disk Accretion of matter can lead to novae and white dwarf supernovae Copyright 2009 Pearson Education Inc 13 2 Neutron Stars Our goals for learning What is a neutron star How were neutron stars discovered What can happen to a neutron star in a close binary system Copyright 2009 Pearson Education Inc What is a neutron star Copyright 2009 Pearson Education Inc A neutron star is the ball of neutrons left behind by a massive star supernova The degeneracy pressure of neutrons supports a neutron star against gravity Copyright 2009 Pearson Education Inc Electron degeneracy pressure goes away because electrons combine with protons making neutrons and neutrinos Neutrons collapse to the center forming a neutron 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 Bell noticed very regular pulses of radio emission coming from a single part of the sky The pulses were coming from a spinning neutron star a pulsar Copyright 2009 Pearson Education Inc Pulsar at center of Crab Nebula pulses 30 times per second Copyright 2009 Pearson Education Inc X rays Crab Nebula Movie CHANDRA Copyright 2009 Pearson Education Inc Visible light Pulsars A pulsar is a neutron star that beams radiation along a magnetic axis that is not aligned with the rotation axis Copyright 2009 Pearson Education Inc Pulsars The radiation beams sweep through space like lighthouse beams as the neutron star rotates Copyright 2009 Pearson Education Inc Neutron Star Limit Quantum mechanics says that neutrons in the same place cannot be in the same state Neutron degeneracy pressure can no longer support a neutron star against gravity if its mass exceeds about 3MSun Copyright 2009 Pearson Education Inc What have we learned What is a neutron star A ball of neutrons left over from a massive star supernova and supported by neutron degeneracy pressure How were neutron stars discovered Beams of radiation from a rotating neutron star sweep through space like lighthouse beams making them appear to pulse Observations of these pulses were the first evidence for neutron stars Copyright 2009 Pearson Education Inc 13 3 Black Holes
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