G'day from the land of ozzzzz
http://arxiv.org/abs/0802.1507
Sheared Flow As A Stabilizing Mechanism In Astrophysical Jets
Authors: Lucas Wanex, Erik Tendeland
(Submitted on 11 Feb 2008 (v1), last revised 11 Feb 2008 (this version, v2))
Abstract: It has been hypothesized that the sustained narrowness observed in the asymptotic cylindrical region of bipolar outflows from Young Stellar Objects (YSO) indicates that these jets are magnetically collimated. The j cross B force observed in z-pinch plasmas is a possible explanation for these observations. However, z-pinch plasmas are subject to current driven instabilities (CDI). The interest in using z-pinches for controlled nuclear fusion has lead to an extensive theory of the stability of magnetically confined plasmas. Analytical, numerical, and experimental evidence from this field suggest that sheared flow in magnetized plasmas can reduce the growth rates of the sausage and kink instabilities. Here we propose the hypothesis that sheared helical flow can exert a similar stabilizing influence on CDI in YSO jets.
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http://arxiv.org/abs/astro-ph/0609344
General Relativistic Magnetohydrodynamic Simulations of Jet Formation with a Thin Keplerian Disk
Authors: Yosuke Mizuno (NSSTC/MSFC/NPP), Ken-Ichi Nishikawa (NSSTC/UAH), Shinji Koide (Kumamoto Univ.), Philip Hardee (UA), Gerald J. Fishman (MSFC)
(Submitted on 13 Sep 2006 (v1), last revised 3 Nov 2006 (this version, v2))
Abstract: We have performed several simulations of black hole systems (non-rotating, black hole spin parameter a=0.0 and rapidly rotating, a=0.95) with a geometrically thin Keplerian disk using the newly developed RAISHIN code. The simulation results show the formation of jets driven by the Lorentz force and the gas pressure gradient. The jets have mildly relativistic speed (\sim 0.4c). The matter is continuously supplied from the accretion disk and the jet propagates outward until each applicable terminal simulation time (non-rotating: t/\tau_S = 275 and rotating: t/tau_S = 200, \tau_S \equiv r_S/c). It appears that a rotating black hole creates an additional, faster, and more collimated matter-dominated inner outflow (\sim 0.5c) formed and accelerated by the twisted magnetic field resulting from frame-dragging in the black hole ergosphere. This is the first known simulation confirming the formation of an inner magnetically-driven, matter-dominated jet by the frame-dragging effect from a black hole co-rotating with a thin Keplerian disk threaded by a vertical magnetic field. This result indicates that jet kinematic structure depends on black hole rotation and on the initial magnetic field configuration and strength.
magnetic field. This result indicates that jet kinematic structure depends on black hole rotation and on the initial magnetic field configuration and strength.
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http://arxiv.org/abs/astro-ph/0505027
Magnetic Tower Outflows from a Radial Wire Array Z-pinch
Authors: S. .V. Lebedev, A. Ciardi, D. Ampleford, S.N. Bland, S.C. Bott, J.P. Chittenden, G. Hall, J. Rapley, A. Frank, E. G. Blackman, T. Lery
(Submitted on 2 May 2005)
We present the first results of high energy density laboratory astrophysics experiments which explore the evolution of collimated outflows and jets driven by a toroidal magnetic field. The experiments are scalable to astrophysical flows in that critical dimensionless numbers such as the Mach number, the plasma beta and the magnetic Reynolds number are all in the astrophysically appropriate ranges. Our experiments use the MAGPIE pulsed power machine and allow us to explore the role of magnetic pressure in creating and collimating the outflow as well as showing the creation of a central jet within the broader outflow cavity. We show that currents flow along this jet and we observe its collimation to be enhanced by the additional hoop stresses associated with the generated toroidal field. Although at later times the jet column is observed to go unstable, the jet retains its collimation. We also present simulations of the magnetic jet evolution using our two-dimensional resistive magneto-hydrodynamic (MHD) laboratory code. We conclude with a discussion of the astrophysical relevance of the experiments and of the stability properties of the jet.
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http://arxiv.org/abs/astro-ph/0409441
Relativistic Jets from Accretion Disks
Authors: R.V.E. Lovelace, P.R. Gandhi, M.M. Romanova
(Submitted on 17 Sep 2004 (v1), last revised 17 Sep 2004 (this version, v2))
Abstract: The jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two main regimes have been discussed, hydromagnetic jets, which have a significant mass flux and have energy and angular momentum carried by both matter and electromagnetic field and, Poynting jets, where the mass flux is small and energy and angular momentum are carried predominantly by the electromagnetic field. Here, we describe recent theoretical work on the formation of relativistic Poynting jets from magnetized accretion disks. Further, we describe new relativistic, fully-electromagnetic, particle-in-cell simulations of the formation of jets from accretion disks. Analog Z-pinch experiments may help to understand the origin of astrophysical jets.
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http://arxiv.org/abs/astro-ph/0108067
Laboratory Astrophysics and Collimated Stellar Outflows: The Production of Radiatively Cooled Hypersonic Plasma Jets
Authors: S.V. Lebedev, J.P. Chittenden, F.N. Beg, S.N. Bland, A. Ciardi, D. Ampleford, S. Hughes, M.G. Haines (Imperial College), A. Frank, E.G. Blackman, T. Gardiner (Univ. of Rochester)
(Submitted on 3 Aug 2001)
Abstract: We present first results of astrophysically relevant experiments where highly supersonic plasma jets are generated via conically convergent flows. The convergent flows are created by electrodynamic acceleration of plasma in a conical array of fine metallic wires (a modification of the wire array Z-pinch). Stagnation of plasma flow on the axis of symmetry forms a standing conical shock effectively collimating the flow in the axial direction. This scenario is essentially similar to that discussed by Canto\' ~and collaborators as a purely hydrodynamic mechanism for jet formation in astrophysical systems. Experiments using different materials (Al, Fe and W) show that a highly supersonic ($M\sim 20$), well-collimated jet is generated when the radiative cooling rate of the plasma is significant. We discuss scaling issues for the experiments and their potential use for numerical code verification. The experiments also may allow direct exploration of astrophysically relevant issues such as collimation, stability and jet-cloud interactions.
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http://arxiv.org/abs/astro-ph/9708142
Instability of toroidal magnetic field in jets and plerions
Authors: Mitchell C. Begelman (JILA, Boulder, USA)
(Submitted on 15 Aug 1997)
Abstract: Jets and pulsar-fed supernova remnants (plerions) tend to develop highly organized toroidal magnetic field. Such a field structure could explain the polarization properties of some jets, and contribute to their lateral confinement. A toroidal field geometry is also central to models for the Crab Nebula - the archetypal plerion - and leads to the deduction that the Crab pulsar's wind must have a weak magnetic field. Yet this `Z-pinch' field configuration is well known to be locally unstable, even when the magnetic field is weak and/or boundary conditions slow or suppress global modes. Thus, the magnetic field structures imputed to the interiors of jets and plerions are unlikely to persist.
To demonstrate this, I present a local analysis of Z-pinch instabilities for relativistic fluids in the ideal MHD limit. Kink instabilities dominate, destroying the concentric field structure and probably driving the system toward a more chaotic state in which the mean field strength is independent of radius (and in which resistive dissipation of the field may be enhanced). I estimate the timescales over which the field structure is likely to be rearranged and relate these to distances along relativistic jets and radii from the central pulsar in a plerion.
I conclude that a concentric toroidal field is unlikely to exist well outside the Crab pulsar's wind termination shock. There is thus no dynamical reason to conclude that the magnetic energy flux carried by the pulsar wind is much weaker than the kinetic energy flux. Abandoning this inference would resolve a long-standing puzzle in pulsar wind theory.
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There is a trend to find what is actually driving the jets and ejecting matter from compact cores such as the so called black holes.
Black holes with singularity I do not think they exist. But! black holes that have a compacted core that acts like a Nucleon and having a mass about 3 or greater than our sun may create electromagnetic fields that may prevent EMR from escaping.
I could be wrong, but! the papers above are not my opinion.
What does this mean to cosmology?
They will have to re-write the standard theory.
A recyclic process may explain all these issues.
Harry : Smile and live another day.