1. 2 vi 2006Bethe Centenary Cornell1 The Future of High Energy Astrophysics Extreme Physics in an Expanding Universe Roger Blandford KIPAC Stanford Hans Bethe Centenary, Cornell

2. 2 vi 2006Bethe Centenary Cornell2 Plan Electromagnetic extraction of energy from black holes Relativistic jets Non-thermal emission Other channels and future possibilities

3. 2 vi 2006Bethe Centenary Cornell3 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 Expansion Extreme Power

4. 2 vi 2006Bethe Centenary Cornell4 Jets are common AGN, GSL, PWN, GRB, YSO… –TeV emission –1 <  < 300 –AGN jets are not ionic? –Jets magnetically confined? –Structured jets –Disk-jet connection ~30c

5. 2 vi 2006Bethe Centenary Cornell5 Black holes common Present in most galaxies –Sc, Irr, Pec? Hole-Bulge Relations –Co-evolution –Influence surroundings Binary black holes –Mergers –Low recoils

6. 2 vi 2006Bethe Centenary Cornell6 Progress - Galactic Center ~100 hot young stars in disk(s) within 10 6 m –Approach ~ 10 4 m mm size<10m? X-ray, infrared flares, QPOs? Non-thermal emission –20 min mm polarization, 10 -8 L edd. Accretion rate<<mass supply Chandra 2-8 keV 2 hours May 2002 campaign: ~0.6-1.2 flares/day

7. 2 vi 2006Bethe Centenary Cornell7 Unipolar Induction B M  V~    P ~ V 2 / Z 0 Crab Pulsar –B ~ 100 MT, ~ 30 Hz, R ~ 10 km –V ~ 30 PV; I ~ 3 x 10 14 A; P ~ 10 31 W Massive Black Hole in AGN –B ~ 1T, ~ 10  Hz, R ~1 Pm –V ~300 EV, I ~ 3EA, P ~ 10 39 W GRB –B ~ 1 TT, ~ 1  Hz, R~10 km –V ~ 30 ZV, I ~ 300 EA, P ~ 10 43 W UHECR: E max ~ ZeV

8. 2 vi 2006Bethe Centenary Cornell8 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

9. 2 vi 2006Bethe Centenary Cornell9 Let there be Light Faraday Maxwell Definition Initial Condition =>Maxwell Tensor, Poynting Flux

10. 2 vi 2006Bethe Centenary Cornell10 Force-Free Condition Ignore inertia of matter  =U M /U P >>  2, 1 Electromagnetic stress acts on electromagnetic energy density Fast and intermediate wave characteristics,

11. 2 vi 2006Bethe Centenary Cornell11 Electromagnetic Formation of Jets For Cygnus A: B ~ 10 4 G; M ~ 10 9 M O E ~   V R in ~ R out ~ 100  I ~ V / R ~ 10 18 A P ~ E I ~ 10 38 W Corotating observer sees energy flow inwards at horizon; conserved energy flux in non-rotating frame is outward.

12. 2 vi 2006Bethe Centenary Cornell12 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? McKinney 2006

13. 2 vi 2006Bethe Centenary Cornell13  X X  B> J X. On the Electrodynamics of Moving Bodies Even field Odd current Camenzind, Koide

14. 2 vi 2006Bethe Centenary Cornell14 Jet Expansion From ~m to 10 6-11 m Initially electro/hydromagnetic –Poynting dominated core Plus pair plasma L EM >>L fluid –MHD disk wind u < 1 Hadrons Where do the currents close? Where does the jet become baryonic?

15. 2 vi 2006Bethe Centenary Cornell15 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 nb DC not AC

16. 2 vi 2006Bethe Centenary Cornell16 Pictor A Current Flow Nonthermal emission is ohmic dissipation of current flow? Electromagnetic Transport 10 18 not 10 17 A DC not AC No internal shocks New particle acceleration mechanisms Pinch stabilized by velocity gradient Equipartition in core Wilson et al

17. 2 vi 2006Bethe Centenary Cornell17 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 X BB I[r] r Return Current P ext << P jet Shear jets stabler than pinches

18. 2 vi 2006Bethe Centenary Cornell18 Simple Example L=L mech +L em =3 x 10 45 (I oo /1EA) 2 erg s -1 I oo =0.15(B/1mG)(r/10pc)EA Equipartition a natural consequence Emission Model Faraday Rotation Model VIPS VLBI survey of 1000 radio sources  I/I 00 P/P 0      L mech L em

19. 2 vi 2006Bethe Centenary Cornell19 Particle acceleration magnetic field amplification and nonthermal emission Shock waves –Non-relativistic –Relativistic Reconnection Electrostatic acceleration Stochastic acceleration Other possibilities

20. 2 vi 2006Bethe Centenary Cornell20 Proton spectrum GeV TeV PeV EeV ZeV ~MWB Energy Density E ~ 50 J c -1fm s -1 c -1km H 0 ~ GRB Energy Density

21. 2 vi 2006Bethe Centenary Cornell21 Supernova Remnants X-ray supernova remnants Shocks Electron acceleration Proton acceleration? TeV gamma rays

22. 2 vi 2006Bethe Centenary Cornell22 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  c  E/E|~  –Second order process dE/dt ~  2 (c/ )E - E/t esc –t acc >r L /c  2 =>Power law distribution function IF, t esc do not depend upon energy –THEY DO!

23. 2 vi 2006Bethe Centenary Cornell23 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) uu / r B u B L

24. 2 vi 2006Bethe Centenary Cornell24 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

25. 2 vi 2006Bethe Centenary Cornell25 Too good to be true! Diffusion: CR create their own magnetic irregularities ahead of shock through instability if >V A –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

26. 2 vi 2006Bethe Centenary Cornell26 Progress - Cosmic Rays Sources of low energy particles t~15Myr,  t>0.1Myr Zevatrons Protons, nuclei, photons GZK cutoff? Bottom up??? ACE

27. 2 vi 2006Bethe Centenary Cornell27 UHE Cosmic Rays L>r L /  ;  =u/c –BL>E 21 G pc=>I>3 x 10 18 E 21 A! –Lateral diffusion P>P EM ~B 2 L 2  c/4  3 x 10 39 E 21 2  -1 W –Powerful extragalactic radio sources,  ~1 Relativistic motion eg gamma ray bursts –P EM ~  2 (E/e  ) 2 /Z 0 ~ (E/e) 2 /Z 0 Radiative losses; remote acceleration site –P mw < 10 36 (L/1pc)W Adiabatic losses –E~  /L Observational association with dormant AGN?

28. 2 vi 2006Bethe Centenary Cornell28 Abundances ● (Li, Be, B)/(C, N, O) ● ~ 10 (E/1GeV) -0.6 g cm -2 ● S(E) ~ E -2.2 ● L ~ U CR M gas c    ~ 3 x 10 40 erg s -1 ~ 0.03 L SNR ~ 0.001L gal

29. 2 vi 2006Bethe Centenary Cornell29 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  2 if elastically scattered Spectrum N(E)~E -2.3     eg Keshet &Waxman

30. 2 vi 2006Bethe Centenary Cornell30 Relativistic collisionless shocks in astrophysics Pulsars + winds (plerions)  ~ 10 6 ?? 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?) Simulations of relativistic collisionless shocks Anatoly Spitkovsky (KIPAC)

31. 2 vi 2006Bethe Centenary Cornell31 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: Simulations of relativistic collisionless shocks Relativistic flow is reflected from a wall and sends a reverse shock through the simulation domain Plasma densityField generation

32. 2 vi 2006Bethe Centenary Cornell32 Shock structure with magnetic field Magnetized perpendicular pair shock Magnetized shock is mediated by Larmor reflections from compressed B field 3D density Spectrum - Maxwellian Pair shocks do not show nonthermal acceleration Is Fermi acceleration really viable in magnetized shocks? pxpx pypy pzpz

33. 2 vi 2006Bethe Centenary Cornell33 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  =0  =0.003  =0.1

34. 2 vi 2006Bethe Centenary Cornell34 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

35. 2 vi 2006Bethe Centenary Cornell35 GeV-TeV electrons in jets T gyro E<  f  ~ 100 MeV => C -1 emission If electrons radiate efficiently on time of flight and  <1 =>Modest electron energies in KN regime =>n(E -1 )  T R<10, P 2, 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…)

36. 2 vi 2006Bethe Centenary Cornell36 Electrostatic Acceleration Establish static potential difference Gaps Double Layers Charge-starved waves (Thompson&Blaes) Aurorae Pulsars P EM > (E/e) 2 /Z 0

37. 2 vi 2006Bethe Centenary Cornell37 Surfing Relativistic wind eg from pulsar V=ExB/B 2 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

38. 2 vi 2006Bethe Centenary Cornell38 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

39. 2 vi 2006Bethe Centenary Cornell39 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 local power laws? kU k k 2N2N 

40. 2 vi 2006Bethe Centenary Cornell40 Observational Ramifications VLBI observations –Characteristic Field Geometry Probe using Faraday rotation measurements –Understand jet composition Pairs vs ionic plasma X-ray/  -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

41. 2 vi 2006Bethe Centenary Cornell41 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  -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…”

42. 2 vi 2006Bethe Centenary Cornell42 Prospects: High Energy Density Physics High Power Lasers - 10 23-25 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

43. 2 vi 2006Bethe Centenary Cornell43 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…

44. 2 vi 2006Bethe Centenary Cornell44 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…