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Outstanding (or “Unsolved”) Problems and Space and Astrophysics

Outstanding (or “Unsolved”) Problems and Space and Astrophysics. Peter H. Yoon University of Maryland, College Park, USA Kyung Hee Univ , Korea. Unsolved Problems in Physics http://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics. Cosmology, and general relativity

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Outstanding (or “Unsolved”) Problems and Space and Astrophysics

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  1. Outstanding (or “Unsolved”) Problems and Space and Astrophysics Peter H. Yoon University of Maryland, College Park, USA Kyung HeeUniv, Korea

  2. Unsolved Problems in Physicshttp://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics • Cosmology, and general relativity • Cosmic inflation, gravitational wave, Baryon asymmetry, dark matter, dark energy, … • Quantum gravity • High energy physics/Particle physics • Higgs mechanism, super symmetry, … • Nuclear physics • Astronomy and astrophysics • Accretion disk jet, coronal heating problem, gamma ray bursts, ultrahigh energy cosmic ray, … • Condensed matter physics • High temperature superconductivity, turbulence, quantum computation, … • Biological physics • Other problems

  3. Accretion disc jets • Why do the accretion discs surrounding certain astronomical objects, such as the nuclei of active galaxies, emit relativistic jets along their polar axes? • Why are there quasi-periodic oscillations in many accretion discs? • Why does the period of these oscillations scale as the inverse of the mass of the central object? • Why are there sometimes overtones, and why do these appear at different frequency ratios in different objects?

  4. 2x109 solar mass black hole Synchrotron jet M87

  5. M87 (Centaurus A) & radio jet superposed

  6. Cygnus A (3C 405) radio & optical image Cygnus A radio jet

  7. Combined HST and VLA image of the galaxy 0313-192. Optical HST image shows the galaxy edge-on; VLA image, shown in red, reveals giant jet of speeding particles. Most radio galaxies are elliptical. This example shows radio jets emanating from a spiral galaxy (wrong galaxy?).

  8. • P. H. Yoon and T. Chang, Collective plasma microinstability as a possible mechanism for the one-sided core jet emission of extragalactic radio sources, Astrophys. J., 343, 31 (1989) • P. H. Yoon and L. F. Ziebell, An Emission Mechanism for Extragalactic Radio Jets, Astrophys. J., 459, 529 (1996).

  9. Coronal heating problem • The temperature of the Sun's surface is at about 5800 kelvin. • The corona is at about 1 to 3 MK (parts of the corona can even reach 10 MK).

  10. Coronal heating theories • Magnetic reconnection (or nanoflares) • Wave heating theory (turbulence)

  11. Magnetic reconnection (or nanoflares)

  12. Reconnection (nanoflares) • The hypothesis of "microflares" as a possible explanation of the coronal heating was first suggested by Gold (1964) and then later developed by Parker (1972). • Nanoflare arises from an event of magnetic reconnection which converts the energy stored in the solar magnetic field into the motion of the plasma.

  13. Reconnection as energy conversion mechanism

  14. The problem with reconnection • Exact energy conversion calculation: P. H. Yoon and A. T. Y. Lui, Exact Energy Principle in Magnetic Reconnection for Current-Sheet Models, PRL, 94, 175004 (2005). • According to this paper, the energy conversion during reconnection is very inefficient!

  15. Stretched (unreconnected) B field Reconncted B field Reduction in the B field energy Energy conversion efficiency is very small (at most a few %) Increase in the particle energy

  16. Problem with reconnection (nanoflare) model • Energy conversion by magnetic reconnection is TOO INEFFICIENT – hence, coronal heating based on reconnection is still not solved.

  17. Wave heating theory (turbulence)

  18. Alfven waves in the solar corona, Tomczyk et al., Science (2007)

  19. Problem with Wave Heating Theory • Alfvén wave frequency is too low and wavelength is too long. • Alfvén waves must first undergo cascade before efficient resonant heating can take place.

  20. Long wavelength, low-frequency Alfven waves cannot heat/accelerate solar charged particles

  21. Turbulent waves can heat/accelerate solar charged particles (wave-particle resonance)

  22. Typical Solar wind turbulence spectrum ffc f–5/3 dB2 f = /2p

  23. Transition to turbulence: Cascade L3 L2 L1

  24. Magnetohydrodynamics (MHD)

  25. Magnetohydrodynamics (MHD) Only wave-wave interaction is described by MHD theory

  26. Cascade direction Cascade direction

  27. Problem with MHD turbulence • MHD theory has no wave-particle interaction. • MHD theory breaks down for high-frequency, short wavelength regime. • (Technical) MHD turbulence predicts perpendicular cascade.

  28. Resolution Requires Kinetic PhysicsKinetic Theory of Magnetized Plasma Turbulence

  29. Preliminary efforts • Reduced kinetic (gyro-kinetic) turbulence theory: • HowesG. G., et al. (2006), Astrophys. J., 651, 590 • Schekochihin, A. A., et al. (2007), Plasma Phys. Control. Fusion, 49, A195 • … • Attempts for fully kinetic turbulence theory: • Tsytovich, V. N. & Shvartsburg, A. B. (1966), Sov. Phys. JETP, 22, 554 • Yoon, P. H. (2007), Phys. Plasmas, 14, 102302 • Yoon, P. H. & Fang, T.-M. (2008), Plasma Phys. Control. Fusion,50, 085007

  30. Wave-wave Wave-particle

  31. MHD Description MHD not valid

  32. Log(i) Magnetosonic Lower-hybrid LH Ion -acoustic i Cyclotron Kinetic Alfven Slow-mode Fast Alfven Log(kvA/i) Log(k^vA/i)

  33. Region of Validity of MHD

  34. Problem with wave-heating (turbulence) model • Kinetic theory of solar wind turbulence (that includes wave-particle as well as wave-wave interaction) DOES NOT YETS EXIST! — hence, coronal heating problem based on wave heating is unsolved!

  35. Conclusion: • Magnetic reconnection (nanoflares) model of coronal heating has a problem because reconnection is too inefficient. • Wave heating (turbulence) model of coronal heating is inconclusive because kinetic theory of solar wind turbulence does not yet exist. • Coronal heating problem is unsolved.

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