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The Future of High Energy Astrophysics Extreme Physics in an Expanding Universe

Roger Blandford KIPAC Stanford. The Future of High Energy Astrophysics Extreme Physics in an Expanding Universe. Hans Bethe Centenary, Cornell. Plan. Electromagnetic extraction of energy from black holes Relativistic jets Non-thermal emission Other channels and future possibilities.

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The Future of High Energy Astrophysics Extreme Physics in an Expanding Universe

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  1. Roger Blandford KIPAC Stanford The Future of High Energy AstrophysicsExtreme Physics in an Expanding Universe Hans Bethe Centenary, Cornell Bethe Centenary Cornell

  2. Plan • Electromagnetic extraction of energy from black holes • Relativistic jets • Non-thermal emission • Other channels and future possibilities Bethe Centenary Cornell

  3. Extreme Power Expansion High Energy Sources • Compact Source • Impulsive or Quasi-steady • White dwarf • Neutron star • Black hole • Massive • Stellar • Outflow • Often ultrarelativistic • Dissipation region • Particle acceleration • Nonthermal emission Bethe Centenary Cornell

  4. Jets are common AGN, GSL, PWN, GRB, YSO… • TeV emission • 1 < G < 300 • AGN jets are not ionic? • Jets magnetically confined? • Structured jets • Disk-jet connection ~30c Bethe Centenary Cornell

  5. Black holes common • Present in most galaxies • Sc, Irr, Pec? • Hole-Bulge Relations • Co-evolution • Influence surroundings • Binary black holes • Mergers • Low recoils Bethe Centenary Cornell

  6. Chandra 2-8 keV 2 hours May 2002 campaign: ~0.6-1.2 flares/day Progress - Galactic Center • ~100 hot young stars in disk(s) within 106m • Approach ~ 104m • mm size<10m? • X-ray, infrared flares, QPOs? • Non-thermal emission • 20 min • mm polarization, 10-8 Ledd. • Accretion rate<<mass supply Bethe Centenary Cornell

  7. B  Unipolar Induction M • V~ n F ~ I Z0; P ~ V2 / Z0 • Crab Pulsar • B ~ 100 MT, n ~ 30 Hz, R ~ 10 km • V ~ 30 PV; I ~ 3 x 1014 A; P ~ 1031W • Massive Black Hole in AGN • B ~ 1T , n ~ 10 mHz, R ~1 Pm • V ~300 EV, I ~ 3EA, P ~ 1039 W • GRB • B ~ 1 TT, n ~ 1 kHz, R~10 km • V ~ 30 ZV, I ~ 300 EA, P ~ 1043 W UHECR: Emax ~ ZeV Bethe Centenary Cornell

  8. Three dynamical approaches • Fluid dynamics +passive field • Fluid velocity, scalar + ram pressure • Classical Electromagnetodynamics • Maxwell stress tensor + Poynting Flux • Relativistic Magnetohydrodynamics • All of the above Real sources require all three approaches Bethe Centenary Cornell

  9. Let there be Light • Faraday • Maxwell • Definition • Initial Condition =>Maxwell Tensor, Poynting Flux Bethe Centenary Cornell

  10. Force-Free Condition • Ignore inertia of matter s =UM/UP>>G2, 1 • Electromagnetic stress acts on electromagnetic energy density • Fast and intermediate wave characteristics, Bethe Centenary Cornell

  11. Electromagnetic Formation of Jets Corotating observer sees energy flow inwards at horizon; conserved energy flux in non-rotating frame is outward. For Cygnus A: B ~ 104 G; M ~ 109 MO E ~ W F ~1020 V Rin ~ Rout ~ 100 W I ~ V / R ~ 1018 A P ~ E I ~ 1038 W Bethe Centenary Cornell

  12. MHD/FF Simulations • Time dependent GR calculations • Causality OK • Power from spin of hole • Collimating ~10 jets to r~1000m • Marginally stable • Jet structured • Entrainment? Bethe Centenary Cornell McKinney 2006

  13. X X X On the Electrodynamics of Moving Bodies <B> W Even field Odd current J . Camenzind, Koide Bethe Centenary Cornell

  14. Jet Expansion • From ~m to 106-11m • Initially electro/hydromagnetic • Poynting dominated core • Plus pair plasma • LEM>>Lfluid • MHD disk wind • u < 1 • Hadrons Where do the currents close? Where does the jet become baryonic? Bethe Centenary Cornell

  15. nb DC not AC The case for large scale magnetic collimation • Many jets do not appear to spread like observed fluid jets • M ~  for fluid jets • Typically equipartition pressure in jet exceeds maximum external gas pressure • Some Faraday rotation evidence for toroidal field Bethe Centenary Cornell

  16. Wilson et al Pictor A Electromagnetic Transport 1018 not 1017 A DC not AC No internal shocks New particle acceleration mechanisms Current Flow Nonthermal emission is ohmic dissipation of current flow? Pinch stabilized by velocity gradient Equipartition in core Bethe Centenary Cornell

  17. I[r] r B X Elementary confinement by toroidal field • Toroidal magnetic field B in jet frame • Current I in rest frame • I=2rB/0 • Static equilibrium • Jet Power • Typically Mech power~ 3-10 EM power Return Current Pext << Pjet Shear jets stabler than pinches Bethe Centenary Cornell

  18. Simple Example Lmech   • L=Lmech+Lem=3 x 1045(Ioo/1EA)2 erg s-1 • Ioo=0.15(B/1mG)(r/10pc)EA • Equipartition a natural consequence • Emission Model • Faraday Rotation Model • VIPS VLBI survey of 1000 radio sources I/I00 P/P0 Lem  Bethe Centenary Cornell

  19. Particle acceleration magnetic field amplificationand nonthermal emission • Shock waves • Non-relativistic • Relativistic • Reconnection • Electrostatic acceleration • Stochastic acceleration • Other possibilities Bethe Centenary Cornell

  20. Proton spectrum ~MWB Energy Density E ~ 50 J c -1fm s-1 c -1km H0 ~ GRB Energy Density Bethe Centenary Cornell GeV TeV PeV EeV ZeV

  21. Supernova Remnants • X-ray supernova remnants • Shocks • Electron acceleration • Proton acceleration? • TeV gamma rays Bethe Centenary Cornell

  22. Traditional Fermi Acceleration • Magnetic field lazy-electric field does the work! • Frame change creates electric field and changes energy • CR bounce off magnetic disturbances moving with speed bc • |DE/E|~b • Second order process • dE/dt ~ b2(c/l)E - E/tesc • tacc>rL/cb2 • =>Power law distribution function IF l, tesc do not depend upon energy • THEY DO! Bethe Centenary Cornell

  23. u u / r u u / r L B B Shock Acceleration • Non-relativistic shock front • Protons scattered by magnetic inhomogeneities on either side of a velocity discontinuity • Describe using distribution function f(p,x) Bethe Centenary Cornell

  24. Transmitted Distribution Function where =>N(E)~E-2 for strong shock with r=4 Consistent with Galactic cosmic ray spectrum allowing for energy-dependent propagation Bethe Centenary Cornell

  25. Too good to be true! • Diffusion: CR create their own magnetic irregularities ahead of shock through instability if <v>>VA • Instability likely to become nonlinear - Bohm limit • Cosmic rays are not test particles • Include in Rankine-Hugoniot conditions • u=u(x) • Acceleration controlled by injection • Cosmic rays are part of the shock • What mediates the shock, • Parallel vs Perpendicular • Firehose? Weibel when low field? Ion skin depth Bethe Centenary Cornell

  26. Progress - Cosmic Rays • Sources of low energy particles • t~15Myr,Dt>0.1Myr • Zevatrons • Protons, nuclei, photons • GZK cutoff? • Bottom up??? ACE Bethe Centenary Cornell

  27. UHE Cosmic Rays • L>rL/b; b=u/c • BL>E21G pc=>I>3 x 1018E21 A! • Lateral diffusion • P>PEM~B2L2bc/4p > 3 x 1039 E212b-1 W • Powerful extragalactic radio sources, b ~1 • Relativistic motion eg gamma ray bursts • PEM ~ G2(E/eG)2/Z0 ~ (E/e)2/Z0 • Radiative losses; remote acceleration site • Pmw < 1036(L/1pc)W • Adiabatic losses • E~G/L • Observational association with dormant AGN? Bethe Centenary Cornell

  28. Abundances • (Li, Be, B)/(C, N, O) •  ~ 10 (E/1GeV)-0.6 g cm-2 • S(E) ~ E-2.2 • L ~ UCR Mgas c ~ 3 x 1040 erg s-1 ~ 0.03 LSNR ~ 0.001Lgal Bethe Centenary Cornell

  29. G 2-1/2 G Relativistic Shock Waves • Not clear that they exist as thin discontinuities • May not be time to establish subshock, magnetic scattering • Weibel instability => large scale field??? • Returning particles have energy x G2 if elastically scattered • Spectrum N(E)~E-2.3 eg Keshet &Waxman Bethe Centenary Cornell

  30. Simulations of relativistic collisionless shocksAnatoly Spitkovsky (KIPAC) Relativistic collisionless shocks in astrophysics • Pulsars + winds (plerions)  ~ 106?? • Extragalactic radio sources  ~ 10 • Gamma ray bursts  > 100 • Galactic superluminal sources  ~ few Open issues: • What is the structure of collisionless shock waves? • Particle acceleration -- Fermi mechanism? Something else? • Generation of magnetic fields (GRB shocks, primordial fields?) Bethe Centenary Cornell

  31. Simulations of relativistic collisionless shocks Why does a collisionless shock exist? Particles are slowed down either by instability (two-stream-like) or by magnetic reflection. Unmagnetized shocks are mediated by Weibel instability, which generates magnetic field: Plasma density Field generation Bethe Centenary Cornell Relativistic flow is reflected from a wall and sends a reverse shock through the simulation domain

  32. Magnetized perpendicular pair shock Shock structure with magnetic field px 3D density py pz Spectrum - Maxwellian Pair shocks do not show nonthermal acceleration Magnetized shock is mediated by Larmor reflections from compressed B field Is Fermi acceleration really viable in magnetized shocks? Bethe Centenary Cornell

  33. =0 =0.003 =0.1 Conclusions • Relativistic collisionless shocks exist, mediated by two-stream instability (Weibel) in low magnetization flows, and coherent reflections in higher magnetization flows. Transition is observed in simulations: • Efficient thermalization of the flow. In magnetized shocks not enough turbulence downstream for nonthermal acceleration. In unmagnetized shocks some evidence for diffusive nonthermal acceleration, although long-term large simulations still need to be done. • Compositionally this suggests weak acceleration efficiency in pair plasma flows. Additional component of the ions may be necessary. 3D density Bethe Centenary Cornell

  34. Is particle acceleration ohmic dissipation of electrical current? • Jets delineate the current flow?? • Organized dominant electromagnetic field • Shocks weak and ineffectual • Tap electromagnetic reservoir • Poynting flux along jet and towards jet • Jet core has equipartition automatically • Automatically have kinetic energy to tap Bethe Centenary Cornell

  35. GeV-TeV electrons in jets • Tgyro < Tsynchrotron =>E<af-1~ 100 MeV => C-1 emission • If electrons radiate efficiently on time of flight and a<1 =>Modest electron energies in KN regime =>n(E-1)sTR<10, P2, relativistic sources quite likely • Not a great challenge! • No strong shocks when magnetically dominated • Must beat radiative loss • Hybrid (+e) bulk acceleration schemes tapping kinetic energy of shear flow (Stern, Poutanen…) Bethe Centenary Cornell

  36. Electrostatic Acceleration • Establish static potential difference • Gaps • Double Layers • Charge-starved waves (Thompson&Blaes) • Aurorae • Pulsars • PEM > (E/e)2/Z0 Bethe Centenary Cornell

  37. Surfing • Relativistic wind eg from pulsar • V=ExB/B2 E->B, V->c • More generally force-free electrodynamics, limit of MHD when inertia ignorable evolves to give regions where E/B increases to, and sometimes through, unity • cf wake-field acceleration Bethe Centenary Cornell

  38. Flares and Reconnection • May be intermittent not steady • Strong, inductive EMF? • Hall effects important • Most energy -> heat • Create high energy tail • Theories are highly controversial! • Relativistic reconnection barely studied at all Bethe Centenary Cornell

  39. Stochastic acceleration • Line and sheet currents break up due to instabilities like filamentation? • Create electromagnetic wave spectrum • Nonlinear wave-wave interactions give electrons stochastic kicks • Inner scale where waves are damped by particles • Are there localpower laws? g2Ng kUk Bethe Centenary Cornell g k

  40. Observational Ramifications • VLBI observations • Characteristic Field Geometry • Probe using Faraday rotation measurements • Understand jet composition • Pairs vs ionic plasma • X-ray/g-ray observations • Are particles accelerated at strong shocks? • Synchrotron vs inverse Compton emission • TeV (HESS/VERITAS) vs GeV (GLAST) • Outside-in or inside-out emission Bethe Centenary Cornell

  41. Prospects:GLAST (2007) • Some key science objectives: • understand particle acceleration and high-energy emission from neutron stars and black holes, including GRBs • determine origin(s) of g-ray extragalactic diffuse background • measure extragalactic background starlight • search for dark matter extra dimensions?n • Multi-wavelength observations • Interpolates discoveries of Chandra/XMM and HESS. “.. GLAST will focus on the most energetic objects and phenomena in the universe…” Bethe Centenary Cornell

  42. Prospects: High Energy Density Physics • High Power Lasers - 1023-25 W m-2 • > MT magnetic field • >100 MeV electron quiver energies • Collisionless shocks, particle acceleration, magnetic field • Spheromaks • Dynamics and stability of force-free configurations • Magnetic reconnection • High current e-beam experiments • Current instabilities • Z-pinches • Stability Bethe Centenary Cornell

  43. Computational Prospects • Major advances in recent years • 3D RMD in Kerr-Schild coordinates! • Increased dynamical range using Adaptive Mesh Refinement • Jets, disks • Improved treatment of energy • Radiative transfer • Kinetic problems… Bethe Centenary Cornell

  44. Summary • Great progress in high energy astrophysics • Big astrophysics problems are multisource not just multiwavelength • Major computational advances • Short term observational prospects very good • Chandra, XMM, Swift, Suzaku… • HESS, MAGIC, (VERITAS?) • Auger • LIGO, Amanda, ICECUBE, NESTOR, Anita, LOFAR • GLAST (2007) • Long term prospects in space problematic • NuSTAR, LISA, Constellation-X, XEUS… Bethe Centenary Cornell

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