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Boom! Within 0.25s core is neutrons with radius 20 km and super-nuclear density Very little light can escape, energy carried off by neutrinos. Power emitted in these exceeds all known stars for 10 s At this density core collapse stops with bounce Colliding with infalling layers this triggers shock wave blowing outer star into space (96% of mass for star) In compressed heated shock wave fusion to Fe and beyond via r- process As ejecta thin light can escape. Luminosity reaches Energy released type-II supernova – gravitational in origin 1

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Seeing Them Sung dynasty history describes a supernova in 1054 whose remnant – Crab nebula in Taurus – is still visible (M1) Japanese, Arabic, Native American records concur Milky Way supernovae also in 1006, 1572, 1604. Estimated every 300 years but obscured by dust Many visible in other galaxies, currently some 20-30 bright ones 2

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SN 2011dh 3

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Classification SN classified by spectrum: – Ia: Strong Si no H He – Ib: Weak H Strong He – Ic: Weak Si no H He – II: Strong H Ia are nuclear explosion of WD II Ib Ic are gravitational core collapse with degrees of envelope loss 4

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168,000 years ago a B3 I supergiant collapsed in LMC Observed as SN 1987A Progenitor known – changed theory Remnants observed in detail 5

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The Nebula 6

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What we are Seeing 7

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Neutrinos Three hours before the supernova detected, neutrino detectors observed a burst (20) of neutrinos from the right direction. 20 detected implies 10 58 emitted carrying 10 46 J in agreement with models Neutrinos get out before shock wave disperses outer layers, so got here before the light Neutrino Astronomy launched, many new experiments planned 8

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What is Left of Core? Electron degeneracy cannot stop collapse – few electrons Neutron degeneracy pressure at density in Surface gravity Physics is relativistic Chandrasekhar Limit depends on rotation Rapid Rotation expected High magnetic field frozen in 9

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Discovery Physics Predictions: – Rapid Rotation – Intense magnetic field – High Temperature Bell 1967: Periodic 1.337s Radio pulses: LGM? Quickly found other sources: natural Soon find many pulsars Slow down in 10

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LGM Data 11

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What are Pulsars? Rotating star breaks up Only NS dense enough to survive Emission aligned to magnetic axis - tilted 12 Crab pulsar : Neutron star SN remnant

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How They Work General Idea: Rapidly changing intense magnetic field creates intense electric field Lifts charged particles from polar regions into magnetosphere dragged around by rotation Accelerated to relativistic speeds – emit synchrotron radiation at all wavelengths in direction of magnetic axis Emitted energy slows rotation Luminosity of Crab nebula agrees with observed rate of slowing of pulsar Pulsars observed in all bands 13

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Principle of Relativity Laws of Physics are the same measured at rest or moving at constant velocity determines accelerations which are the same in both frames At rest is meaningless. Only relative velocities are physical 14

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This Week Follow Principle of Relativity as far as it takes us Electromagnetism will force some modifications – Special Relativity Find that Newtonian gravity is not invariant after all Describe General Relativity and some Astronomically important consequences Black Holes 15

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Space and Time Space: All possible positions Motion described by Plot on three axes to produce worldline Spacetime: All possible events Newton I: Objects upon which no forces act have straight worldlines 16

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Spacetime Velocity is slope of worldline from axis Stationary objects have vertical worldlines Horizontal line (space) is Universe at some time 17

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Relativity in Spacetime O’ moves at relative to O Describe same event by different coordinates 18

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Velocity Addition 19

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Maxwell’s Problem Maxwell’s equations predict the speed of electromagnetic waves in terms of measured properties of electric and magnetic interactions Electromagnetism is not invariant under Galilean relativity 20

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Two Possible Solutions Light propagates at through aether Maxwell’s equations hold for observers at rest relative to aether Moving at measure Light propagates at through space Maxwell’s equations hold for all inertial observers Moving at measure 21

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Looking for the Aether A light clock is two mirrors at distance Light bounces between them in time Moving light clock relative to aether will change its rate 22

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Two Motions Moving along axis Moving transversely 23

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The Answer Michelson-Morley 1887: Viscous aether dragged by Earth? Einstein 1905: No Aether. Maxwell’s equations hold in any inertial frame Galilean relativity is wrong. 24

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Lorentz Transformations Send a light pulse from Seek 25

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Lorentz Transformations 26

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The Answer 27 For and not too large,

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The Answer 28 Note or else this makes no sense

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Simultaneity Most unintuitive: Simultaneity is Relative Is causality lost? Source of many “paradoxes” 29 Measure distance in light-seconds or time in light-meters so

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Time and Simultaneity Since we know is constant we can measure time of distant events If light from reaches 0 at time it was emitted at The present: Events from which light will reach us at 30

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Length Contraction A ruler lies at This is 31

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Time Dilation Clock at ticks at 32

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Doppler Doppler formula modified by time dilation – Transverse Doppler effect – Longitudinal Doppler effect 33

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Is This Real? We have lots of experimental evidence This is real. Any ruler constructed using Lorentz-invariant physics will contract at high speed. Any physical clock will run slow at high speed 34

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Velocity Addition 35

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The Invariant Interval Lorentz transformations have the property that 36 lightcone

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What It Means If an observer with gets to is proper time If observer comes from This is future/past 37 past future

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What it Means If observer with finds is proper distance Faster observer has order reversed Causal theory means no material particle or information can propagate faster than 38 past future

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Conservation Laws Newtonian conservation laws are not Lorentz- invariant Find relativistic conserved quantities 39

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Remarks 40 invariant mass transform under Lorentz like These conservation laws hold always. Lavoisier 1777 would find that energy lost to radiation reduced mass slightly Decay of a particle that does not conserve mass is consistent with these – and happens Other conserved quantities are invariant

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Relativistic Laws Electromagnetism (Maxwell) is Lorentz-invariant Nuclear interactions have Lorentz-invariant form Quantum relativistic version (Quantum Field Theory 1940/1972. Gravity???? 41

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