共查询到20条相似文献，搜索用时 46 毫秒
1.
B. C. Tewari 《Astrophysics and Space Science》2012,342(1):73-77
A new class of exact solutions of Einstein’s equations is proposed for a collapsing radiating spherically symmetric shear-free isotropic fluid undergoing radial heat flow. In remote past the solutions are static perfect fluid which then gradually starts evolving into radiating collapse. The interior solutions are matched with Vaidya exterior metric over the boundary. 相似文献
2.
X-ray radiation is used to study coronal phenomena in conjunction with meter wave observations during some large solar flares. It is found that metric flare continua and moving type IV bursts are associated with gradual and long lasting (a few tens of minutes) microwave and hard X-ray emissions. The detailed temporal analysis reveals that although metric and hard X-ray sources are located at very different heights, both kinds of emission result from a common and continuous/repetitive injection of electrons in the corona. The late part of the metric event (stationary type IV burst) is only associated with soft X-ray radiation. This indicates that the mean energy of the radiating electrons is lower during stationary type IV bursts than during the earlier parts of the event. 相似文献
3.
W. Barreto 《Astrophysics and Space Science》1993,201(2):191-201
The influence of viscosity on the gravitational collapse in radiating fluid spheres is investigated. The interior solution is matched with the Vaidya metric at the boundary of the fluid distribution. Prescribing an equation of state to take into account the degree of induced anisotropy by the viscosity and using the Herrera, Jiménez and Ruggeri method, we obtain an explicit Tolman VI-like exploding model. The sphere explodes more violently when the anisotropy due to the viscosity is smaller. The shear viscosity diminishes with the expansion of the distribution of matter. 相似文献
4.
An axially symmetric space time is considered in the presence of a perfect fluid source in Barbers (Gen. Relativ. Gravit.
14, 117, 1982) second self creation theory of gravitation. An exact radiating cosmological model is presented using a relation
between the metric potentials. Some physical and kinematical properties of the model are also discussed. 相似文献
5.
Kesh S. Govinder Megan Govender & Roy Maartens 《Monthly notices of the Royal Astronomical Society》1998,299(3):809-810
Relativistic models of radiating stellar collapse with shear require careful checking of all the equations and quantities involved. We illustrate this by showing that, in a recently proposed model, the metric ansatz is in fact too restrictive to allow any radial evolution to occur, and only tangential evolution is possible. Furthermore, the assumption of pressure isotropy is shown to reduce the model to the static case without radiation or shear. 相似文献
6.
7.
In this paper we formulate the problem of the collapse of a spherically-symmetric, radiating body in general relativity. The requirement that the metric and its normal derivative be continuous across the boundary imposes conditions upon the evolution of the star and allows identification of physical phenomena measured by a distant observer. A solution to Einstein's field equations for the exterior of a spherically-symmetric radiating body is that derived originally by Vaidya in 1951. By requiring the continuity described above we identify the mass, luminosity, velocity, and time increment measured by a distant observer in terms of the metric parameters evaluated in a frame comoving with the outer boundary. We also assume that the interior metric is a sum of products of functions of the radius and time. The continuity requirements allow the evolution of two of the three functions of time to be determined. The evolution of the third function, describing the motion of the core, is determined by the imposition of an equation of state at the center. The adiabatic index derived from the Baym-Bethe-Pethick equation of state was used to provide this last equation. A major result is obtaining an analytic solution to Einstein's field equations describing the core of a collapsing star. As a consequence of this solution we found that for the relatively small values of the adiabatic index (max1.6), the star smoothly made the transition to a final collapsed state. Neither bounce nor shock wave was obtained. Also, there is a readily understood connection between the adiabatic index, and such parameters of the edge of the core as the velocity and acceleration. Finally, the analytic solutions provide the time-scales for the collapse which are significantly different from that of free-fall. The retarding effects of pressure upon the collapse are apparent. It is hoped that such analytic solutions will provide insight into more complicated dynamic systems in general relativity. 相似文献
8.
In this paper we present a new class of nonsingular solutions representing time dependent balls of perfect fluid with matter-radiation
in general relativity. The solution of the class is suitable for interior modeling of a quasar i.e. a massive radiating star.
The interior solution is matched with a zero pressure Vaidya metric. From this solution we constructed a quasar model by assuming
the life time of the quasar of ≈107 year. We obtained a mass of the quasar of ≈109 M
θ
, linear dimension ≈1017 km and a rate of emission L
∞≈1047 erg/s. 相似文献
9.
Z. Yousaf 《Astrophysics and Space Science》2018,363(11):226
The aim of this study is to analyze the role of modification of gravity on some dynamical properties of spherically symmetric relativistic systems. In this settings, the mathematical modeling of scalar variables associated with the shearing viscous dissipative anisotropic spherical stars is explored. We assume that the non-static diagonally symmetric spherical structure is coupled with a relativistic matter content in the presence of \(f(G,T)=\alpha G^{n}+\beta \ln [G]+\lambda T\) gravity. After using Misner–Sharp mass function, we have made correspondence between metric scale factors, tidal forces and structure parameters. We have adopted Herrera’s technique for the orthogonally breaking down of the Riemann tensor, in order to formulate modified forms of structure scalars. The role of these invariants is then explored in the evolutionary properties of radiating spheres. The parameters responsible for the outbreak of inhomogeneities are being examined in the presence and absence of constant \(f(G,T)\) terms. It is inferred that the evolutionary phases of the spherical interiors can be well studied via extended versions of scalar variables. 相似文献
10.
11.
Detailed mapping in a 14,000,000 km2 area of northwestern Guinevere Planitia and northern Beta Regio bounded by 264°-312°E, 24°-60°N has revealed thousands of long extensional lineaments (graben, fissures and related fractures). These can be grouped into radiating, circumferential and linear systems. Thirty four radiating systems have been identified, of which 16 have radii greater than 300 km and eight have radii greater than 1000 km. Twenty six linear (straight) systems with a length greater than 300 km have been distinguished of which six have a length greater than 1000 km. Linear systems are generally associated with rifts, although some may represent distal portions of radiating systems. In addition, 19 circumferential systems, some associated with coronae, have been identified. The distribution of each system is compared with the host geology in order to place the graben-fissure systems in a regional stratigraphic framework. The majority of systems are: (1) younger than tesserae, ridge belts and densely fractured plains, (2) coeval with, and in many cases, define fracture belts, (3) partially flooded by wrinkle-ridged plains units, and (4) older than smooth and lobate plains units and young rifts. The inventory of radiating graben-fissure systems that we catalogue represents a database of tectono-magmatic centers that complements the centers defined using other criteria, e.g., large volcanoes, coronae, and shield fields. We have attempted to identify those systems that are underlain by dike swarms in order to evaluate their relationship to mantle plumes. At least 11 of the radiating systems extend well beyond any central topographic uplift and are therefore interpreted to be underlain by dike swarms. 相似文献
12.
Koijam Manihar Singh 《Astrophysics and Space Science》2010,325(2):293-302
Investigations are made on slowly rotating radiating Universes coupled with a scalar field in the spherically symmetric Einstein
formalism, and some new interesting solutions are obtained. Their physical and geometrical properties are studied from various
angles. The rotational perturbations of such models are examined in order to substantiate the possibility that the universe
is endowed with some rotation. The nature and role of the metric rotation as well as that of the rotation of matter are studied,
and the effects of radiation and scalar fields on them are discussed. The models here turn out to be rotating as well as expanding
ones, which may be taken as good examples of real astrophysical objects in this universe. The periods of the physical validity
and the restrictions on the radii of the models for real astrophysical situations are obtained and discussed. The models obtained
here are theoretically satisfactory and therefore there is a possibility that there may be less known objects in this universe
which may be represented by our model Universes obtained here and many unknown properties of this universe may be explored
and unfolded in the study of these models. 相似文献
13.
E. Falize C. Michaut C. Cavet S. Bouquet M. Koenig B. Loupias A. Ravasio C. G. Gregory 《Astrophysics and Space Science》2009,322(1-4):71-75
In this paper we study specific classes of radiating shocks which are widely spread in astrophysical environments. We present new analytical solutions available for any exponents of typical power-law cooling function which generalize the five special cases (corresponding to specific values of these exponents) of radiating shocks structure and proceed to the analytical determination of physical quantities. Then an application of the results for the accretion shock in polar is realized. A discussion of the reproducibility of cooling layer in laboratory is proposed using scaling laws. 相似文献
14.
Data from spectrophotometric observations in the 485-1105 nm range at different times are used to determine the basic physical
parameters of the continuum radiating layer of L2 Pup: spectrophotometric temperatures, radii, and velocities of recession from the star's center. The phase dependences of
these parameters over a cycle, during which the temperature varied from 2300 to 2900 K and the variations in radius were as
high as 60%, are determined. The radius of the radiating layer is seen to vary irregularly, the radius of the layer is found
to depend on wavelength, and the variations in the expansion velocity are evaluated.
Translated from Astrofizika, Vol. 52, No. 1, pp. 99–115 (February 2009). 相似文献
15.
We analyze the statistical distribution of weakly radiating pulsars, i.e., radio pulsars that have passed to the stage of an orthogonal rotator during the evolution of the inclination angle X. We discuss in detail the factors that lead to a significant reduction in the energy losses for this class of objects. We have determined the number of weakly radiating radio pulsars and their distribution in spin period P. The predictions of a theory based on the model of current losses are shown to be consistent with observational data. 相似文献
16.
17.
Wang Yong-jiu 《Chinese Astronomy and Astrophysics》1984,8(4):283-285
In this paper, a metric containing five arbitrary functions of time is obtained which describes the gravitational field of an arbitrary accelerated and charged point-mass (star). It is a further generalization of Vaidya's star metric, [1]. In particular cases, it reduces to the Reissner-Nortström metric and the Kinnersley metric [2]. Since the various parameters of the source can vary arbitrarily in time, this metric is of wide applicability and may prove to be useful for various specific astronomical objects. 相似文献
18.
The synchrotron mechanism of radiation from the Crab pulsar has been investigated on the assumption that the mechanism acts in a source moving with relativistic velocity round a neutron star. A detailed matching has been made of the theoretical spectra of synchrotron radiation from relativistic electrons with the results of measurements of the radiation flux from the Crab pulsar in the infrared, optical and X-ray ranges. The parameters of the radiating region (intensity of the magnetic field, source dimensions, density and lifetime of radiating electrons) have been found. They are expressed through the ratio of the energy density of the magnetic field in the source to that of radiating electrons. The level of Compton-radiation in this region is estimated. Possible values of at which the level will correspond to the available results of measurements of the-radiation flux from the Crab pulsar are given. An estimate is presented for the surface magnetic field of the neutron star which does not contradict those obtained from considerations of the magnetic flux conservation when compressing the object up to the neutron star dimensions. 相似文献
19.
The effect of the finite extent of the optically radiating region of SS433 is investigated. Light travel time effects are small, but a slightly improved fit to the observational data can be obtained with a dimension ofl o?1015 cm for the optical jets. 相似文献
20.
N. F. Vojkhanskaja 《Astrophysical Bulletin》2017,72(2):191-198
We investigate the question of the possible variable conditions in dwarf novae. The Balmer decrements are used as variability indicators due to their form being strongly dependent on the conditions in the radiating medium. It is shown that the decrements are usually anomalous and variable in time at minimum light, which indicates a variability of the conditions in the radiating medium. The spectrum changes significantly during the outburst state, the decrement becomes steep and has no anomalies. It appears that the outburst makes the emitting region more homogeneous and sparse. Another possible explanation is that the radiation is emitted by some other region, unseen at minimum light. 相似文献