Exact relativistic model for a superdense star

Assuming that the physical 3-spacet = const in a superdense star is spheroidal, a static spherically symmetric model based on an exact solution of Einstein’s equations is given which will permit densities of the order of 2 × 10¹⁴ gm cm^-3, radii of the order of a few kilometers and masses up to about four times the solar mass.     

Hannay angles for relativistic polar orbits around an oblate spheroid

The Hannay adiabatic angles are computed for polar orbits in the gravitational field of an oblate spheroid described in the post-Newtonian framework of general relativity.     

Differential rotation of relativistic superfluid in neutron stars

It is shown how to set up a mathematically elegant and fully relativistic superfluid model that can provide a realistic approximation (neglecting small anisotropies due to crust solidity, magnetic fields, etc., but allowing for the regions with vortex pinning) of the global structure of a rotating neutron star, in terms of just two independently moving constituents. One of these represents the differentially rotating neutron superfluid, while the other part represents the combination of all the other ingredients, including the degenerate electrons, the superfluid protons in the core, and the ions in the crust, the electromagnetic interactions of which will tend to keep them locked together in a state of approximately rigid rotation. Order of magnitude estimates are provided for relevant parameters such as the resistive drag coefficient.     

Numerical construction of magnetosphere with relativistic two-fluid plasma flows

We present a numerical model in which a cold pair plasma is ejected with relativistic speed through a polar cap region and flows almost radially outside the light cylinder. Stationary axisymmetric structures of electromagnetic fields and plasma flows are self-consistently calculated. In our model, motions of positively and negatively charged particles are assumed to be determined by electromagnetic forces and inertial terms, without pair creation and annihilation or radiation loss. The global electromagnetic fields are calculated by the Maxwell's equations for the plasma density and velocity, without using ideal magnetohydrodynamic condition. Numerical result demonstrates the acceleration and deceleration of plasma due to parallel component of the electric fields. Numerical model is successfully constructed for weak magnetic fields or highly relativistic fluid velocity, i.e. kinetic energy dominated outflow. It is found that appropriate choices of boundary conditions and plasma injection model at the polar cap should be explored in order to extend present method to more realistic pulsar magnetosphere, in which the Poynting flux is dominated.     

Structure and stability of rotating fluid disks around massive objects. II. General relativistic formulation

In this paper we have considered the structure of a thick perfect fluid disk of constant density rotating around a Schwarzschild black hole and its stability under axisymmetric perturbation. The inner edge of such disk cannot lie within 4m. The critical γ_c for neutral stability is found to be much less than 4/3 indicating that the disks are generally stable     

时频系统中主备钟一致性保持方法的研究1

为保证主、备钟切换时时间信号的准确性和稳定性,开展了主、备钟一致性保持方法的研究。搭建了进行主、备钟一致性保持的实验系统,阐述了系统的原理,分析了不同钟差预测模型的效果,给出了计算备份钟频率补偿量的公式,测试了系统在不同控制周期下的同步水平。测试结果表明：采用本系统的主、备钟一致性保持方法,能够实现主、备钟间的最大时间偏差小于1 ns的指标,同时提高了备份钟的长期频率稳定度。     

Theoretical aspects of relativistic spectral features

The inner parts of black‐hole accretion discs shine in X‐rays which can be monitored and the observed spectra can be used to trace strong gravitational fields in the place of emission and along paths of light rays. This paper summarizes several aspects of how the spectral features are influenced by relativistic effects. We focus our attention onto variable and broad emission lines, origin of which can be attributed to the presence of orbiting patterns – spots and spiral waves in the disc. We point out that the observed spectrum can determine parameters of the central black hole provided the intrinsic local emissivity is constrained by theoretical models. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

General relativistic effects in the γ-ray radiation from pulsars

General relativistic and quantum-mechanical effects in the γ-ray radiation from neutron stars are studied in this paper. For three values of the magnetic dipole moment, we calculated the upper limit of the escaping energy of the γ-photon as a function of the angle between the line of sight and the magnetic axis, with and without these effects. We conclude that for low magnetic moments, the quantum-mechanical effects are unimportant but the general relativistic effects are to reduce significantly the upper limit. For high magnetic moments, the two effects nearly cancel out and the net effect is small. We discuss the implications of these results on the γ-ray spectrum.     

时间、距离、速度、红移基本物理概念的演变简史

为了尝试回答“我们能否观测到退行速度超过光速的星系”这一问题,重新考察了在牛顿物理学、狭义相对论、广义相对论和宇宙学中的时伺、距离、速度和红移等概念．揭开了一些错误观念的实质,发现只要摆脱狭义相对论先入为主的束缚,上述问题即可迎刃而解．强调了宇宙学并不是纯粹的广义相对论,而是该理论在服从宇宙学原理的条件下的一个特例,其中一系列基本物理概念都因此得到新的内涵。     

Limit shocks of relativistic magnetohydrodynamics

In this paper we show that switch-on and switch-off shocks are allowed by the shock equations of relativistic MHD and have similar properties to their Newtonian counterparts. Just like in Newtonian MHD they are limits of fast and slow shock solutions and as such they may be classified as weakly evolutionary shocks.     

Gravitational waves: The future of black hole physics

The new millennium will witness the operation of several long-baseline ground-based interferometric detectors, possibly a space-based detector too, which will make it possible to directly observe black holes by catching gravitational waves emitted by them during their formation or when they are perturbed or when a binary consisting of black holes in-spirals due to radiation reaction. Such observations will help us not only to test some of the fundamental predictions of Einstein's general relativity but will also give us the unique opportunity to map black hole spacetimes, to measure the masses and spins of black holes and their population, etc.     

Gravitational singularities via acceleration: The case of the Schwarzschild solution and Bach's gamma metric

The so called gamma metric corresponds to a two‐parameter family of axially symmetric, static solutions of Einstein's equations found by Bach. It contains the Schwarzschild solution for a particular value of one of the parameters, that rules a deviation from spherical symmetry. It is shown that there is invariantly definable singular behaviour beyond the one displayed by the Kretschmann scalar when a unique, hypersurface orthogonal, timelike Killing vector exists. In this case, a particle can be defined to be at rest when its world‐line is a corresponding Killing orbit. The norm of the acceleration on such an orbit proves to be singular not only for metrics that deviate from Schwarzschild's metric, but also on approaching the horizon of Schwarzschild metric itself, in contrast to the discontinuous behaviour of the curvature scalar.     

A Solution of Einstein's Field Equations fora Tachyonic Gas: Possible Astrophysical Applications

In this paper we show that a change in the signs of some of the metric components of the solution of the field equations for the classical cosmic string results in a solution which we interpret as a time-dependent wall composed of tachyons. We show that the walls have the property of focusing the paths of particles which pass through them. As an illustration of this focusing, we demonstrate the results of a simple simulation of the interaction between one such tachyon wall and a rotating disk of point masses. This interaction leads to the temporary formation of spiral structures. These spiral structures exist for a time on the order of one galactic rotation. This revised version was published online in July 2006 with corrections to the Cover Date.     

A source for the Reissner-Nordstrøm metric

An exact solution of the coupled Einstein-Maxwell equations representing the gravitational field in the interior of a sphere of charged incoherent matter in equilibrium is obtained which is a charged analogue of the static perfect fluid sphere solution with spheroidal 3-space obtained by Vaidya & Tikekar.     

The Universe Evolution as Possible Mechanism of Formation of Galaxies and Their Clusters

The Kepler problem is studied in a space with the Friedmann-Lemaitre-Robertson-Walker metrics of the expanding universe. Cosmic evolution leads to decreasing energy of particles, causing free particles to be captured in bound states, so that the evolution of the universe can be treated as a possible mechanism of the formation of galaxies and clusters of galaxies. The cosmological model is considered where the evolution of the universe plays the role usually inscribed to cold dark matter.     

铯原子喷泉钟均匀C场的实现

C场均匀度是影响铯原子喷泉钟性能的重要因素。为了消除漏磁等对磁场均匀度的影响,加入补偿线圈,通过用最小二乘法计算,逐次得出补偿线圈的个数、位置与电流。实验表明：计算数据与实验结果吻合,得到c场不均匀性小于2nT、长度达48cm的均匀区。     

Stability of general relativistic Miyamoto–Nagai galaxies

The stability of a recently proposed general relativistic model of galaxies is studied in some detail. This model is a general relativistic version of the well-known Miyamoto–Nagai model that represents well a thick galactic disc. The stability of the disc is investigated under a general first-order perturbation keeping the space–time metric frozen (no gravitational radiation is taken into account). We find that the stability is associated with the thickness of the disc. We find that flat galaxies have more non-stable modes than the thick ones, i.e. flat galaxies have a tendency to form more complex structures like rings, bars and spiral arms.