The origin of the substantial magnetic fields that are found in galaxies and on even larger scales, such as in clusters of galaxies, is yet unclear. If the second-order couplings between photons and electrons are considered, then cosmological density fluctuations, which explain the large-scale structure of the universe, can also produce magnetic fields on cosmological scales before the epoch of recombination. By evaluating the power spectrum of these cosmological magnetic fields on a range of scales, we show here that magnetic fields of 10(-18.1) gauss are generated at a 1-megaparsec scale and can be even stronger at smaller scales (10(-14.1) gauss at 10 kiloparsecs). These fields are large enough to seed magnetic fields in galaxies and may therefore have affected primordial star formation in the early universe.

In this letter, we discuss generation of magnetic field from cosmological perturbations. We consider the evolution of three component plasma (electron, proton and photon) evaluating the collision term between elecrons and photons up to the second order. The collision term is shown to induce electric current, which then generate magnetic field. There are three contributions, two of which can be evaluated from the first-order quantities, while the other one is fluid vorticity which is purely second order. We estimate the magnitudes of the former contributions and shows that the amplitude of the produced magnetic field is about ∼ 10 −19 G at 10Mpc comoving scale at the decoupling. Compared to astrophysical and inflationary mechanisms for seed-field generation, our study suffers from much less ambiguities concerning unknown physics and/or processes.

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We study generation of magnetic fields by the Biermann mechanism in the supernova explosions of first stars. The Biermann mechanism produces magnetic fields in the shocked region between the bubble and interstellar medium (ISM), even if magnetic fields are absent initially. We perform a series of two-dimensional magnetohydrodynamic simulations with the Biermann term and estimate the amplitude and total energy of the produced magnetic fields. We find that magnetic fields with amplitude 10 −14 − 10 −17 G are generated inside the bubble, though the amount of magnetic fields generated depend on specific values of initial conditions. This corresponds to magnetic fields of 10 28 − 10 31 erg per each supernova remnant, which is strong enough to be the seed magnetic field for galactic and/or interstellar dynamo.Subject headings: magnetic fields -cosmology: interstellar medium -supernova remnant IntroductionMagnetic fields are ubiquitous in the universe. In fact, observations of rotation measure and synchrotron radiation have revealed that magnetic fields exist in astronomical objects

The synthesis of vertically aligned carbon nanotubes with submillimeter-order heights was performed using ethanol chemical vapor deposition with Co catalysts supported on Al 2 O 3 substrates. The effects of Al 2 O 3 in the form of amorphous alumina and single-crystalline sapphire were investigated through a characterization of the Co catalyst particles on the substrates. An important effect of Al 2 O 3 was found to be the production of highly dense and nanosized Co particles, owing to a low surface diffusivity.

We developed a magneto-turbulent model for the cosmic ray (CR) electrons seen in the radio halo clusters of galaxies. Steady state momentum distribution functions of the CR electrons are calculated for given spectra of the turbulent Alfvén waves. The radio spectrum produced by the obtained CR electron distribution is compared to the observed radio spectrum of the Coma radio halo. We find that the observed radio spectrum of the Coma cluster is well reproduced when the spectral index of the turbulent Alfvén waves is ∼ 2.8. The obtained energy spectrum of the turbulent Alfvén waves is steeper than that expected from the turbulence theory, suggesting back reaction of the particle acceleration. The fitting procedure constraints the amplitude of the turbulent Alfvén waves as well as the spectral index. Then we estimate the dissipation of the turbulent Alfvén waves, which is found to be less than the cooling rate by X-ray radiation. We suggest that the turbulence which is sufficient for particle acceleration is developed in the clusters containing the radio halo. It is most likely that cluster mergers create the turbulence and seed relativistic electrons. Kim et al. (1990) studied the magnetic fields in the Coma cluster by using the rotation measures (RMs) of background radio sources (QSO and radio galaxies). The observed RMs of the background sources seen through the Coma cluster have an excess of ∼ 38 rad m −2 . By adopting a galaxy scale of 10−40 kpc as a correlation length, they found the (electron density weighted) amplitude of the random magnetic field to be ∼ 1 µG. On the other hand, the comparison between nonthermal hard X-ray emission and synchrotron radio emission gives the volume averaged magnetic field strength, if all the hard X-ray is emitted through inverse Compton scattering of CMB photons (Rephaeli 1979). Rephaeli, Gruber, & Rothschild (1987) obtained a lower limit value ∼ 0.11 µG by using the upper limit on the hard X-ray emission from the Coma cluster. The first detection of the hard X-ray emission from the Coma cluster by BeppoSAX gives the field strength of 0.15 µG (Fusco-Femiano et al. 1999).

We present a Monte Carlo model of He ii reionization by quasi‐stellar objects (QSOs, quasars) and its effect on the thermal state of the clumpy intergalactic medium (IGM). The model assumes that patchy reionization develops as a result of the discrete distribution of QSOs. It includes various recipes for the propagation of the ionizing photons, and treats photoheating self‐consistently. The model predicts the fraction of He iii, the mean temperature in the IGM, and the He ii mean optical depth – all as a function of redshift. It also predicts the evolution of the local temperature versus density relation during reionization. Our findings are as follows. The fraction of He iii increases gradually until it becomes close to unity at z∼ 2.8–3.0. The He ii mean optical depth decreases from τ∼ 10 at z≳ 3.5 to τ≲ 0.5 at z≲ 2.5. The mean temperature rises gradually between z∼ 4 and z∼ 3 and declines slowly at lower redshifts. The model predicts a flattening of the temperature–density relation, with significant increase in the scatter during reionization at z∼ 3. Towards the end of reionization, the scatter is reduced and a tight relation is re‐established. This scatter should be incorporated in the analysis of the Lyα forest at z≲ 3. Comparison with observational results of the optical depth and the mean temperature at moderate redshifts constrains several key physical parameters.

The cluster abundance and its redshift evolution are known to be powerful tools for constraining the amplitude of mass fluctuations 8 and the mass density parameter m0 . We study the impact of the finite decay rate of cold dark matter particles on the cluster abundances. On the basis of a spherical model in a decaying cold dark matter universe, we calculate the mass function of clusters and compare it with observed cluster abundance. We find the decay of cold dark matter particles significantly changes the evolution of the cluster abundance. In particular, we point out that the lifetime of dark matter particles comparable to the age of the universe lowers the ratio of the local cluster abundance to the high-redshift cluster abundance and can account for the observed evolution of the cluster abundance quite well. The strong dependence of the cluster abundance on the decay rate of dark matter suggests that distant cluster surveys may offer clues to the nature of dark matter.