Zhang Jia-lü

Spectra of radiation for spinless and spin relativistic particles in strong magnetic fields

Synchro-curvature radiation put forward by Zhang and Cheng is a new and universal radiation mechanism, it describes in detail the radiation properties of a relativistic charged particle moving in a curved magnetic field. This new radiation generalizes all the classical results of ordinary synchrotron and curvature radiations and reveals inherent linkage and unification between them. Additionly, a general, simple and unitary formula is provided for discussing the radiation problem in research of pulsars. However, the magnitude of the magnetic field of a pulsar is so strong (107-109T) that the quantum effects cannot be neglected. The GFWW method developed recently by Lieu and Axford is applied to generalize the results of Zhang and Cheng. The quantum limited synchro-curvature radiation spectra for spinless K-G particles and spin-1/2 Dirac particles are presented, respectively. Their radiation properties are also discussed.

Line profiles of radially moving clouds in the presence of an accretion disk

Abstract In the black hole model of active galactic nuclei, light rays emitted by ionized clouds moving in the vicinity of the black hole will be subjected to the effects of doppler shift, gravitational redshift and bending, as well as shielding by accretion disk, should this exist. We have taken all these effects into consideration in a rigorous solution of the photon transport equation for the line profile under the Schwarzschild metric. It is found that asymmetric double peak structure appears in some cases.

Cosmic strings and the two-point galaxy-galaxy correlation function

Abstract We calculated the two-point galaxy-galaxy correlation function ξ within the cosmic string model and compared with the observed result of Davis and Peebles [1] and found that the model can satisfactorily explain the observed ξ-curve. One interesting result is that, using the cosmic string scenario, one can naturally obtain a feature that other cosmological models have difficulty in accounting for, namely, the “bend” of the 1 + ξ curve at r c ≈ 3 h −1 Mpc, when the exponent in the power law changes from −2 to −0.85, [2].

The Raman spectrum of the T Tauri star LkHαl20

Abstract Raman scattering may play an important role in astrophysics since it has been successfully used in interpreting some unidentified emission lines. In this paper we examined the spectral data of the T Tauri star LkHαl20 and estimated the Raman scattering cross-sections and the line intensities. We found that the unidentified lines of this star, λλ 4200.9, 5098.1, 5613.9, 5768.0, 6633.5, 6667.0, 7500.0A are very probably the Raman spectrum generated when the FeI and FeII line series are scattered by H atoms and H 2 and CO molecules.

The second and third moments of Abell clusters and their three-point correlation function

Abstract Using the method of counts in cells we calculated the second and third moments in the angular distribution of northern Abell clusters with richness classes ⩾ 1 and hence their spatial three-point correlation. We also calculated the three-point correlation function for a redshift sample of D ⩽4, R ⩾1 Abell clusters, the results are in agreement with those obtained for samples with estimated redshifts, thus showing further that the three-point correlation function of galaxies and Abell clusters can be described by a universal form.

Cosmic strings: Large-scale mass fluctuations and velocity fields

Abstract In this paper we calculate the large scale mass fluctuations and peculiar velocity fields in the cosmic string scenario in different dark matter-dominated universes. By using Turok et al.s string density fluctuation spectra before gravitational growth and the usual linear perturbation theory, we get the mean square root mass fluctuation 〈( δM M ) 2 (M)〉 1 2 and obtain the first calculation of large-scale peculiar velocity fields in the cosmic string picture. If we assume galaxies trace the mass distribution, normalization of δM/M at scale 8 Mpch−1 requires Gμ > 10−5, which is too large to be allowed by Big Bang nucleosynthesis theory and the observed background radiation anisotropy, where μ is the mass per unit string length. Pancaking at z = 3 in neutrino-dominated universes requires even larger Gμ. The peculiar velocity decreases more slowly with increasing distance than in usual cosmological models, but this is still not enough to explain Collins et al.s observed data. Our results indicate that cosmic string density fluctuations alone cannot form such large scale structures as observed.

The variation of the angle between the magnetic and rotation axes in a collapsing star

Abstract We derive the formula for the variation of the magnetic axis in a collapsing oblique rotator. Our results of calculation show that the case of the magnetic axis coincident with the rotation axis is unstable, and the angle between the two axes will grow on any small perturbation.

Apparent superluminal expansion in a quasar neutrino halo

We deduce the apparent velocity formula of general relativity for a source moving in a spherical neutrino halo and show that, considering gravitational effects on the motion of photons, the neutrino halo around a quasar may cause apparent superluminal phenomena. Sample calculations illustrating this result are shown.

Temperature profile of accretion disk around a kerr black hole

Abstract We use a rigorous, general relativistic, viscous, fluiddynamical equation to calculate the temperature profile of the accretion disk around a Kerr black hole. Our result shows that there is indeed a maximum in the profile. If the radiation in the disk is black-body radiation, then the result is independent of the viscosity mechanism. Using a free-free radiation and the Lα viscosity law, our results are similar to our previous findings [1]. Our calculation also shows that within the radius of the temperature maximum, there exists a rapidly cooling ring-shaped region, possessing characteristics that are not found in the case with the usual temperature profile.

Projected star density surrounding a black hole in a star cluster

Abstract We discuss, on the basis of general relativity, the density distribution of stars around a black hole at the centre of a globular cluster. We show that the radial density profile depends on the ratio of specific heats γ and the results by Peebles and by Bahcall and Wolf are particular cases with γ ⩽ 4 3 . We give also the projected density profiles, obtained by numerical integration, for ready comparison with observations.