Origins of Cosmic magnetism

2018 ◽  
Vol 14 (A30) ◽  
pp. 291-294
Author(s):  
Kandaswamy Subramanian
Keyword(s):  
Kinetic Energy ◽  
Magnetic Fields ◽  
Early Universe ◽  
Magnetic Energy ◽  
Turbulent Dynamo ◽  
Degree Of Coherence ◽  
Seed Field ◽  
Standard Picture

AbstractThe standard picture for the origin of magnetic fields in astrophysical systems involves turbulent dynamo amplification of a weak seed field. Dynamos convert kinetic energy of motions to magnetic energy. While it is relatively easy for magnetic energy to grow, explaining the observed degree of coherence of cosmic magnetic fields generated by turbulent dynamos, remains challenging. We outline potential resolution of these challenges. Another intriguing possibility is that magnetic fields originated at some level from the early universe.

scholarly journals Turbulent dynamo in a collisionless plasma

2016 ◽  
Vol 113 (15) ◽  
pp. 3950-3953 ◽  
Author(s):  
François Rincon ◽  
Francesco Califano ◽  
Alexander A. Schekochihin ◽  
Francesco Valentini
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Energy ◽  
Collisionless Plasma ◽  
High Energy ◽  
Nearby Galaxy ◽  
Astrophysical Plasmas ◽  
Flow Energy ◽  
Field Amplification ◽  
Turbulent Dynamo

Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.

scholarly journals Magnetic Field Generation within Molecular Clouds

1993 ◽  
Vol 157 ◽  
pp. 429-430
Author(s):  
A. Lazarian
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Molecular Complexes ◽  
Magnetic Field Generation ◽  
Field Problem ◽  
Field Generation ◽  
Internal Motions ◽  
Turbulent Dynamo ◽  
Seed Field

Magnetic field generation in molecular (atomic) clouds at the early stages of galactic evolution is considered. It is shown that if there is no internal motions immersed the cloud, battery mechanisms (Lazarian 1992a) can account for the generation of thin magnetic shells around clouds insides in plasma with temperature gradients. If turbulent motions are present, the dynamo can be essential. The operation of α — ω, α2 and turbulent dynamos within molecular clouds is discussed. It is shown that the turbulent dynamo leads to generation of magnetic fields in the trace behind the cloud. These magnetic fields within the molecular clouds and in their vicinity are important for the solution of the galactic seed field problem (see Lazarian 1992b) and the formation of structures in clumpy molecular complexes.

scholarly journals Magnetic Fields in the Early Universe

2002 ◽  
Vol 12 ◽  
pp. 727-728 ◽  
Author(s):  
Martin Rees
Keyword(s):  
Magnetic Fields ◽  
Early Universe ◽  
Stellar Winds ◽  
Seed Field

AbstractIt is argued that the seed field from the galactic dynamo comes from the first supernovae or stellar winds, or perhaps from early AGNs.

Evolution of Turbulent Magnetic Fields – Approach to a Steady State

1971 ◽  
Vol 43 ◽  
pp. 487-504
Author(s):  
S. Nagarajan
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Magnetic Fields ◽  
Magnetic Energy ◽  
Dynamical Evolution ◽  
Magnetic Excitation ◽  
Electrically Conducting ◽  
Electrically Conducting Fluid ◽  
Turbulent Dynamo ◽  
Magnetic Spectrum

The dynamical evolution of a weak, random, magnetic excitation in a turbulent electrically-conducting fluid is examined under varying kinematic conditions. It is found that the results of an earlier paper (Kraichnan and Nagarajan, 1967) can be reliably extended to a stage of evolution wherein the magnetic spectrum has reached local equipartition with the velocity. The transfer of the magnetic energy to smaller wavenumbers (larger scales) is considerable and significant. This result is highly pertinent to the turbulent dynamo question, which has been variously investigated recently. The relevance of the coupling of the rms magnetic field to the magnetic modes of all scales in deciding the efficiency of this transfer is discussed.

The macrodynamics of α-effect dynamos in rotating fluids

1975 ◽  
Vol 67 (3) ◽  
pp. 417-443 ◽  
Author(s):  
W. V. R. Maekus ◽  
M. R. E. Proctor
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Magnetic Energy ◽  
Finite Amplitude ◽  
Small Scale ◽  
Past Study ◽  
Ohmic Loss ◽  
General Will ◽  
Rotating Systems ◽  
Stellar Magnetic Fields

Past study of the large-scale consequences of forced small-scale motions in electrically conducting fluids has led to the ‘α-effect’ dynamos. Various linear kinematic aspects of these dynamos have been explored, suggesting their value in the interpretation of observed planetary and stellar magnetic fields. However, large-scale magnetic fields with global boundary conditions can not be force free and in general will cause large-scale motions as they grow. I n this paper the finite amplitude behaviour of global magnetic fields and the large-scale flows induced by them in rotating systems is investigated. In general, viscous and ohmic dissipative mechanisms both play a role in determining the amplitude and structure of the flows and magnetic fields which evolve. In circumstances where ohmic loss is the principal dissipation, it is found that determination of a geo- strophic flow is an essential part of the solution of the basic stability problem. Nonlinear aspects of the theory include flow amplitudes which are independent of the rotation and a total magnetic energy which is directly proportional to the rotation. Constant a is the simplest example exhibiting the various dynamic balances of this stabilizing mechanism for planetary dynamos. A detailed analysis is made for this case to determine the initial equilibrium of fields and flows in a rotating sphere.

Fully developed MHD turbulence near critical magnetic Reynolds number

1981 ◽  
Vol 104 ◽  
pp. 419-443 ◽  
Author(s):  
J. Léorat ◽  
A. Pouquet ◽  
U. Frisch
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Isotropic Turbulence ◽  
Magnetic Energy ◽  
Reynolds Numbers ◽  
Magnetic Reynolds Number ◽  
Mhd Equations ◽  
Liquid Sodium ◽  
Turbulent Heat ◽  
Mhd Turbulence

Liquid-sodium-cooled breeder reactors may soon be operating at magnetic Reynolds numbers RM where magnetic fields can be self-excited by a dynamo mechanism (as first suggested by Bevir 1973). Such flows have kinetic Reynolds numbers RV of the order of 107 and are therefore highly turbulent.This leads us to investigate the behaviour of MHD turbulence with high RV and low magnetic Prandtl numbers. We use the eddy-damped quasi-normal Markovian closure applied to the MHD equations. For simplicity we restrict ourselves to homogeneous and isotropic turbulence, but we do include helicity.We obtain a critical magnetic Reynolds number RMc of the order of a few tens (non-helical case) above which magnetic energy is present. RMc is practically independent of RV (in the range 40 to 106). RMc can be considerably decreased by the presence of helicity: when the overall size of the flow L is much larger than the integral scale l0, RMc can drop below unity as suggested by an α-effect argument. When L ≈ l0 the drop can still be substantial (factor of 6) when helicity is a maximum. We examine how the turbulence is modified when RM crosses RMc: presence of magnetic energy, decreased kinetic energy, steepening of kinetic-energy spectrum, etc.We make no attempt to obtain quantitative estimates for a breeder reactor, but discuss some of the possible consequences of exceeding RMc, such as decreased turbulent heat transport. More precise information may be obtained from numerical simulations and experiments (including some in the subcritical regime).

scholarly journals DECAY OF MAGNETIC FIELDS IN THE EARLY UNIVERSE

2003 ◽  
Author(s):  
MARK HINDMARSH ◽  
M. CHRISTENSSON ◽  
A. BRANDENBURG
Keyword(s):  
Magnetic Fields ◽  
Early Universe

scholarly journals Generation and Amplification of Magnetic Fields in the Early Universe

2002 ◽  
Vol 12 ◽  
pp. 709-711 ◽  
Author(s):  
James M. Stone
Keyword(s):  
Magnetic Fields ◽  
Early Universe ◽  
Initial Seed

AbstractA very brief review is given of processes that may be responsible for the generation of initial seed magnetic fields in the early Universe, and that can amplify those fields to the levels observed in galaxies in the current epoch.

scholarly journals Sturm und Drang: The turbulent, magnetic tempest in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 395-398
Author(s):  
Brian C. Lacki
Keyword(s):  
Magnetic Fields ◽  
Galactic Halo ◽  
Galactic Center ◽  
Termination Shock ◽  
Strong Magnetic Fields ◽  
Random Forcing ◽  
Sturm Und Drang ◽  
Turbulent Dynamo ◽  
Starburst Regions

AbstractThe Galactic center central molecular zone (GCCMZ) bears similarities with extragalactic starburst regions, including a high supernova (SN) rate density. As in other starbursts like M82, the frequent SNe can heat the ISM until it is filled with a hot (∼ 4 × 107 K) superwind. Furthermore, the random forcing from SNe stirs up the wind, powering Mach 1 turbulence. I argue that a turbulent dynamo explains the strong magnetic fields in starbursts, and I predict an average B ∼70 μG in the GCCMZ. I demonstrate how the SN driving of the ISM leads to equipartition between various pressure components in the ISM. The SN-heated wind escapes the center, but I show that it may be stopped in the Galactic halo. I propose that the Fermi bubbles are the wind's termination shock.

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