Non-Gaussian cosmic microwave background temperature fluctuations from peculiar velocities of clusters     

Naoki Yoshida †  Ravi K. Sheth  Antonaldo Diaferio 《Monthly notices of the Royal Astronomical Society》2001,328(2):669-677

We use numerical simulations of a (480 Mpc  h ⁻¹)³ volume to show that the distribution of peak heights in maps of the temperature fluctuations from the kinematic and thermal Sunyaev–Zeldovich (SZ) effects will be highly non-Gaussian, and very different from the peak-height distribution of a Gaussian random field. We then show that it is a good approximation to assume that each peak in either SZ effect is associated with one and only one dark matter halo. This allows us to use our knowledge of the properties of haloes to estimate the peak-height distributions. At fixed optical depth, the distribution of peak heights resulting from the kinematic effect is Gaussian, with a width that is approximately proportional to the optical depth; the non-Gaussianity comes from summing over a range of optical depths. The optical depth is an increasing function of halo mass and the distribution of halo speeds is Gaussian, with a dispersion that is approximately independent of halo mass. This means that observations of the kinematic effect can be used to put constraints on how the abundance of massive clusters evolves, and on the evolution of cluster velocities. The non-Gaussianity of the thermal effect, on the other hand, comes primarily from the fact that, on average, the effect is larger in more massive haloes, and the distribution of halo masses is highly non-Gaussian. We also show that because haloes of the same mass may have a range of density and velocity dispersion profiles, the relation between halo mass and the amplitude of the thermal effect is not deterministic, but has some scatter.  相似文献   

Separation Problem in Satellite Gravimetry     

SHEN Wenbin NING Jinsheng 《地球空间信息科学学报》2007,10(1):4-11

The problem of separating gravitation from inertia is discussed in very general sense, and the conclusion is positive: man can separate gravitation from inertia, if various observation techniques are applied for. The accelerometer's position problem in satellite gravimetry is investigated, and the additional acceleration effect due to the position error of an instrument as well as the difference between the mass center and the gravity center is explored.  相似文献   

Quantum Vacuum Effects in the Gravitational Field of a Global Monopole     

A. A. Saharian 《Astrophysics》2004,47(2):260-272

A study is made of the vacuum expectation values for the energy-momentum tensor of a massive scalar field that satisfy a Robin mixed boundary condition on a spherical surface with a background gravitational field from a D+1-dimensional global monopole. Expressions are derived for the Wightman function, vacuum expectation of the square of the field, vacuum energy density, and the radial and azimuthal pressures inside the spherical surface. The regularization procedure involves using the generalized Abel-Plana formula for series in terms of the zeroes of cylindrical functions. This formula makes it possible to separate the part owing to the gravitational field of a global monopole without boundaries from the vacuum expectation and to represent the parts induced by the boundary in the form of exponentially converging integrals which are especially convenient for numerical calculations. The asymptotic behavior of the vacuum averages is studied at the center of the sphere and near its surface. It is shown that for small values of the parameter describing the solid-angle deficit in the geometry of a global monopole, the vacuum stresses induced by the boundary are highly anisotropic.  相似文献   

Saa有挠引力模型下慢旋转磁中子星的电磁场     

陈次星  张家铝 《天文学报》2004,45(2):141-157

导出在Saa有挠引力模型下慢旋转磁中子星电磁场所满足的方程，并研究其外部解，得出如下结论：其一，选规范．A^0=0，电磁场存在某种形式的特解；其二，选规范A^0≠0，电磁场根本不存在此特解．故可通过观测中子星外部电磁场的形式判断挠率是否存在．  相似文献   

The Terrain Correction in a Moving Tangent Space     

Grafarend  E.W.  Hanke  S. 《Studia Geophysica et Geodaetica》2001,45(3):211-234

Conventionally the terrain/topographic reduction is based on the Bouguer Plate, which is flat and extends in the local tangent plane/horizontal plane to infinity. Here we aim at an error estimate of such a planar approximation of the Newton integral of the type of a disturbing potential and gravitational disturbance as linearized forms of the gravitational potential and the modulus of gravitational field intensity. To effect this quality control of the conventional terrain reduction, we first transform the spherical Newton functional from an equatorial frame of reference to an oblique meta-equatorial frame of reference with the evaluation point as a meta-North pole, and then by means of an oblique equiareal map projection of the azimuthal type to a tangent plane which moves at the evaluation point. The first term of these transformed Newton functionals is the planar approximation. The difference between the exact Newton kernels and their planar approximation are plotted and tabulated in Tables 1-3. Three configurations are studied in detail: for points at radius r = 10 km around the evaluation point the systematic error varies from 0.26% for a spherical height difference of the order of H – H* = 5 km, more than 0.80% for a spherical height difference of the order of H – H* = 1 km, and more than 1.60% for a spherical height difference of H – H* = 500 m. In contrast, the systematic error for spherical height difference H – H* = 1 km at a distance of r = 1000 km from the evaluation point increases to 44%. Indeed, the newly derived exact Newton kernels which are of the convolution type and are represented in the tangent space moving with the evaluation point can be preferably used with little extra computational effort.  相似文献   

On the least action principle in cosmology     

Adi Nusser  Enzo Branchini 《Monthly notices of the Royal Astronomical Society》2000,313(3):587-595

Given the present distribution of mass tracing objects in an expanding universe, we develop and test a fast method for recovering their past orbits using the least action principle. In this method, termed FAM for fast action minimization, the orbits are expanded in a set of orthogonal time basis functions satisfying the appropriate boundary conditions at the initial and final times. The conjugate gradient method is applied to locate the extremum of the action in the space of the expansion coefficients of the orbits. The treecode gravity solver routine is used for computing the gravitational field appearing in the action and the potential field appearing in the gradient of the action. The time integration of the Lagrangian is done using Gaussian quadratures. FAM allows us to increase the number of galaxies over previous numerical action principle implementations by more than one order of magnitude. For example, orbits for the 15 000 IRAS PSC z galaxies can be recovered in 12 000 CPU seconds on a 400-MHz DEC-Alpha machine. FAM can recover the present peculiar velocities of particles and the initial fluctuations field. It successfully recovers the flow field down to cluster scales, where deviations of the flow from the Zel'dovich solution are significant. We also show how to recover orbits from the present distribution of objects in redshift space by direct minimization of a modified action, without iterating the solution between real and redshift spaces.  相似文献   

Gravitational wave signals from the collapse of the first stars     

R. Schneider  A. Ferrara  B. Ciardi  V. Ferrari  S. Matarrese † 《Monthly notices of the Royal Astronomical Society》2000,317(2):385-390

We study the gravitational wave emission from the first stars, which are assumed to be very massive objects (VMOs). We take into account various feedback (both radiative and stellar) effects regulating the collapse of objects in the early Universe and thus derive the VMO initial mass function and formation rate. If the final fate of VMOs is to collapse, leaving very massive black hole remnants, then the gravitational waves emitted during each collapse would be seen as a stochastic background. The predicted spectral strain amplitude in a critical density cold dark matter (CDM) universe peaks in the frequency range ν ≈5×10⁻⁴–5×10⁻³ Hz, where it has a value in the range ≈10⁻²⁰–10⁻¹⁹ Hz^−1/2, and might be detected by the Laser Interferometer Space Antenna ( LISA ). The expected emission rate is roughly 4000 event yr⁻¹, resulting in a stationary discrete sequence of bursts, i.e. a shot-noise signal.  相似文献   

A method for detecting gravitational waves coincident with gamma-ray bursts     

M. T. Murphy  J. K. Webb  I. S. Heng 《Monthly notices of the Royal Astronomical Society》2000,316(3):657-664

The mechanism for gamma-ray bursters and the detection of gravitational waves (GWs) are two outstanding problems facing modern physics. Many models of gamma-ray bursters predict copious GW emission, so the assumption of an association between GWs and gamma-ray bursts (GRBs) may be testable with existing bar GW detector data. We consider Weber bar data streams in the vicinity of known GRB times and present calculations of the expected signal after co-addition of 1000 GW/GRBs that have been shifted to a common zero time. Our calculations are based on assumptions concerning the GW spectrum and the redshift distribution of GW/GRB sources that are consistent with current GW/GRB models. We discuss further possibilities of GW detection associated with GRBs in light of future bar detector improvements and suggest that co-addition of data from several improved bar detectors may result in detection of GWs (if the GW/GRB assumption is correct) on a time-scale comparable to the LIGO projects.  相似文献   

Gravitational lensing by stars with angular momentum     

M. Sereno 《Monthly notices of the Royal Astronomical Society》2003,344(3):942-950

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Changes in Rotational Angular Momentum due to Gravitational Interactions between Two Finite Bodies*     

D.J. Scheeres 《Celestial Mechanics and Dynamical Astronomy》2001,81(1-2):39-44

Interactions between an initially uniformly rotating body with a second degree and order gravity field and a sphere are analyzed. Explicit predictions of the change in rotational angular momentum of the non-spherical body are derived over one interaction (i.e. periapsis passage) between the bodies. The estimated changes are expressed in terms of trigonometric functions and generalized Hansen coefficients.  相似文献