共查询到20条相似文献,搜索用时 15 毫秒
1.
We examine the behaviour of accretion flow around a rotating black hole in presence of cooling. We obtain global flow solutions
for various accretion parameters that govern the accreting flow. We show that standing isothermal shock wave may develop in
such an advective accretion flow in presence of cooling. This shocked solution has observational consequences as it successfully
provides the possible explanations of energy spectra as well as generation of outflows/jets of various galactic and extra-galactic
black hole candidates. We study the properties of isothermal shock wave and find that it strongly depends on the cooling efficiency.
We identify the region in the parameter space spanned by the specific energy and specific angular momentum of the flow for
standing isothermal shock as a function of cooling efficiencies and find that parameter space gradually shrinks with the increase
of cooling rates. Our results imply that accretion flow ceases to contain isothermal shocks when cooling is beyond its critical
value. 相似文献
2.
For multi-dimensional cosmological models we investigate the dynamics of both, scales and dimensions. The classical equation of motions and the corresponding Wheeler-de Witt equation are set up generally and the qualitative behaviour of the system is discussed for some specific model with 2 factor spaces: A space M1 with dynamical dimension, and a compact internal space M2 of constant dimension. With a natural choice of some contraint, there exist a solution where M1 expands as usual space while M2 is shrinking down to unobservable scales. 相似文献
3.
Jared M. Maruskin 《Celestial Mechanics and Dynamical Astronomy》2010,108(3):265-274
In this paper we derive an explicit, analytic formula for the geodesic distance between two points in the space of bounded
Keplerian orbits in a particular topology. The specific topology we use is that of a cone passing through the direct product
of two spheres. The two spheres constitute the configuration manifold for the space of bounded orbits of constant energy.
We scale these spheres by a factor equal to the semi-major axis of the orbit, forming a linear cone. This five-dimensional
manifold inherits a Riemannian metric, which is induced from the Euclidean metric on
\mathbbR6{\mathbb{R}^6}, the space in which it is embedded. We derive an explicit formula for the geodesic distance between any two points in this
space, each point representing a physical, gravitationally bound Keplerian orbit. Finally we derive an expression for the
Riemannian metric that we used in terms of classical orbital elements, which may be thought of as local coordinates on our
configuration manifold. 相似文献
4.
Universal expressions are presented for spectral characteristics of non-thermal cosmic radio sources which show maxima of
the spectral density of radiation at specific frequencies (negative slopes spectra). For a number of quasars, radio galaxies
and their individual details the most probable physical processes in space leading to spectra of the kind are determined,
and some parameters of the space medium, magnetic field and angular sizes of compact radio sources are estimated. 相似文献
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8.
Soumen Mondal Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2006,371(3):1418-1426
Standing, propagating or oscillating shock waves are common in accretion and winds around compact objects. We study the topology of all possible solutions using the pseudo-Kerr geometry. We present the parameter space spanned by the specific energy and angular momentum and compare it with that obtained from the full general relativity to show that the potential can work satisfactorily in fluid dynamics also, provided the polytropic index is suitably modified. We then divide the parameter space depending on the nature of the solution topology. We specifically study the nature of the standing Rankine–Hugoniot shocks. We also show that as the Kerr parameter is increased, the shock location generally moves closer to the black hole. In future, these solutions can be used as guidelines to test numerical simulations around compact objects. 相似文献
9.
A. A. Saharian 《Astrophysics》1999,42(2):222-233
Homogeneous and Isotropic cosmological models of effective string theory with a curved space are investigated by the methods
of the qualitative theory of dynamical systems. It is shown that for radiation-dominated models, tthe corresponding dynamical
system can be integrated exactly for the general case of dilaton coupling functions. Models in the tree approximation with
a two-dimensional phase space are considered separately. In the general case of loop corrections, all possible stationary
points are found and their character is determined. The results are illustrated using a specific example. Various cases of
fixing the dilaton within the framework of the Damour-Polyakov mechanism are considered.
Translated from Astrofizika, Vol. 42, No. 2, pp. 295–310, April–June, 1999. 相似文献
10.
The properties of quintom model are investigated in the isotropic and homogeneous universe as a dynamical system dominated by dark energy including the phantom and quintessence fields. A general discussion about the phase space of spatially non-flat universe is presented. We study the results for the later times without assuming the specific form of the potential. Then, we exhibit an obvious structure for the dynamics of the system. 相似文献
11.
Based on monoenergetic proton beam tests of both NaI and CsI, a method for estimating the spallation background, due to the cosmic ray protons and trapped protons, has been developed. Comparisons between the calculated background noise and those measured by telescopes on board satellites are made. Good agreements of these comparisons demonstrate that the approach is capable of providing realistic estimates for specific space borne gamma-ray telescopes in well defined orbits. 相似文献
12.
Santabrata Das Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2008,389(1):371-378
We study the dynamical structure of a cooling dominated rotating accretion flow around a spinning black hole. We show that non-linear phenomena such as shock waves can be studied in terms of only three flow parameters, namely the specific energy , the specific angular momentum (λ) and the accretion rate of the flow. We present all possible accretion solutions. We find that a significant region of the parameter space in the plane allows global accretion shock solutions. The effective area of the parameter space for which the Rankine–Hugoniot shocks are possible is maximum when the flow is dissipation-free. It decreases with the increase of cooling effects and finally disappears when the cooling is high enough. We show that shock forms further away when the black hole is rotating compared to the solution around a Schwarzschild black hole with identical flow parameters at a large distance. However, in a normalized sense, the flow parameters for which the shocks form around the rotating black holes are produced shocks closer to the black hole. The location of the shock is also dictated by the cooling efficiency in that higher the accretion rate , the closer is the shock location. We believe that some of the high-frequency quasi-periodic oscillations may be due to the flows with higher accretion rate around the rotating black holes. 相似文献
13.
《天文和天体物理学研究(英文版)》2016,(2)
An optical survey is the main technique for detecting space debris. Due to the specific characteristics of observation, the pointing errors and tracking errors of the telescope as well as image degradation may be significant, which make it difficult for astrometric calibration. Here we present an improved method that corrects the pointing and tracking errors, and measures the image position precisely. The pipeline is tested on a number of CCD images obtained from a 1-m telescope administered by Xinjiang Astronomical Observatory while observing a GPS satellite. The results show that the position measurement error of the background stars is around 0.1 pixel, while the time cost for a single frame is about 7.5 s; hence the reliability and accuracy of our method are demonstrated. In addition, our method shows a versatile and feasible way to perform space debris observation utilizing non-dedicated telescopes, which means more sensors could be involved and the ability to perform surveys could be improved. 相似文献
14.
L. I. Dorman M. E. Katz Yu. I. Fedorov B. A. Shakhov 《Astrophysics and Space Science》1983,94(1):43-95
A consistent theory of energy exchange between high-energy charged cosmic-ray particles and the random inhomogeneities of a magnetic field frozen in the moving solar wind plasma is developed. It is shown that the mode of the particle energy variations at a given law of plasma velocity variation in space is determined by the specific form of the particle distribution function. The equation for the density of cosmic-ray energy is obtained. Consideration is given to the generation of a charged particle energy spectrum in the course of multiple scatterings by the random inhomogeneities of the magnetic field. 相似文献
15.
Historically, our understanding of the solar magnetic field has been shaped by an interplay between theoretical ideas about the subsurface dynamo and precise measurements of magnetic flux at the level of the photosphere. Today we have an unprecedented ability to measure, or to infer from measurements, properties of the magnetic field at every level from the solar interior to interplanetary space, although photospheric observations still lead the way in completeness and precision. I review the state of our capabilities to measure or calculate the magnetic field and suggest that the next major goal should be to follow specific magnetic structures in space and time from before they emerge until they can no longer be detected at any level. 相似文献
16.
In recent years a number of missions have been conceived to acquire and track signals from GPS satellites at altitudes higher
than the GPS constellation itself. The main purpose of SDR is to reduce the number of hardware components, projected for specific
unmodifiable uses, and utilize general purpose units: on board CPU, DSP or FPGA. In this paper he study and design of a GNSS
Software Receiver for space application, applied to a Lunar Mission, is presented with particular attention on Space Segment
device and on Ground Facilities. 相似文献
17.
Radiation exposure and Mission Strategies
for Interplanetary Manned Missions (REMSIM) 总被引:1,自引:0,他引:1
C. Cougnet N. B. Crosby S. Eckersley C. Foullon V. Guarnieri S. Guatelli D. Heynderickx A. Holmes-Siedle C. Lobascio S. Masiello P. Nieminen G. Parisi P. Parodi M. A. Perino M. G. Pia R. Rampini P. Spillantini V. Tamburini E. Tracino 《Earth, Moon, and Planets》2004,94(3-4):279-285
Cosmic radiation is an important problem for human interplanetary missions. The “Radiation Exposure and Mission Strategies for Interplanetary Manned Missions–REMSIM” study is summarised here. They are related to current strategies and countermeasures to ensure the protection of astronauts from radiation during interplanetary missions, with specific reference to: radiation environment and its variability; radiation effects on the crew; transfer trajectories and associated fluences; vehicle and surface habitat concepts; passive and active shielding concepts; space weather monitoring and warning systems. 相似文献
18.
Charged particles emission in a magnetic field on the basis of Boltzman equation with source term is studied. The work develops the results of Narasimha (1962), where the neutral gas expansion into a vacuum is studied. The different specific cases of emission are given for moving sources. The results may be of use when we study phenomena which happen in plasma close to the Earth and in space, as well as for studies of phenomena which take place due to moving satellites in the ionosphere and in interplanetary or interstellar plasma. 相似文献
19.
Fumihiko Usui Shogo Nishida & Yoshiharu Eriguchi 《Monthly notices of the Royal Astronomical Society》1998,301(3):721-728
We have computed line profiles from self-gravitating toroids around black holes. The specific angular momentum of the toroids is assumed to be constant in space. The images of the toroids show peculiar features in the far sides of the black holes. Concerning the line profiles, the red wing extends to the very low frequency region because the location of the inner edge is rather near the event horizon of the black hole and consequently the velocity of the inner edges of the toroids can be greater than that of the Kepler discs. 相似文献
20.
H. M. Tovmassian R. Kh. Hovhannessian R. A. Epremian 《Astrophysics and Space Science》1994,213(2):175-183
Using the results of observations of the Carina nebula made with the space telescope Glazar, it is shown that the extinction law for the nebula is abnormal and that there is a single OB star complex within the nebula at a distance of about 2200 pc. It is suggested that the observed distribution of OB stars in the nebula and also the appearance of the nebula itself is due to a specific structure of the absorbing clouds within the nebula, and that the absorbing clouds may have such structure as a result of an explosion in the center of the nebula. 相似文献