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

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, Estimated every 300 years but obscured by dust Many visible in other galaxies, currently some bright ones 2

SN 2011dh 3

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

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

The Nebula 6

What we are Seeing 7

Neutrinos Three hours before the supernova detected, neutrino detectors observed a burst (20) of neutrinos from the right direction. 20 detected implies emitted carrying 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

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

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

LGM Data 11

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

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

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

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

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

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

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

Velocity Addition 19

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

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

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

Two Motions Moving along axis Moving transversely 23

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

Lorentz Transformations Send a light pulse from Seek 25

Lorentz Transformations 26

The Answer 27 For and not too large,

The Answer 28 Note or else this makes no sense

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

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

Length Contraction A ruler lies at This is 31

Time Dilation Clock at ticks at 32

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

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

Velocity Addition 35

The Invariant Interval Lorentz transformations have the property that 36 lightcone

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

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

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

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

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