共查询到20条相似文献，搜索用时 31 毫秒
1.
The overall dynamical evolution and radiation mechanism of γ-ray burst (GRB) jets are briefly introduced. Various interesting
topics concerning beaming in GRBs are discussed, including jet structures, orphan afterglows and cylindrical jets. The possible
connection between GRBs and neutron stars is also addressed. 相似文献
2.
X. Ribeyre P. Nicolaï S. Galera V. T. Tikhonchuk 《Astrophysics and Space Science》2009,322(1-4):85-90
Supersonic plasma jets are ubiquitous in astrophysics. Our study focus on the jets emanated from Herbig-Haro (HH) objects. They have velocities of a few hundred km/s and are extending over the distances more than a parsec. Interaction of the jets with surrounding matter produces two specific structures in the jet head: the bow shock and the Mach disk. The radiative cooling of these shocks affects strongly the jet dynamics. A tool to understand the physics of these jets is the laboratory experiment. A supersonic jet interaction with surrounding plasma was studied on the PALS laser facility. A collimated high-Z plasma jet with a velocity exceeding 400 km/s was generated and propagated over a few millimeters length. Here we report on study the effect of radiative cooling on the head jet structure with a 2D radiative hydrodynamic code. The simulation results demonstrated the scalability of the experimental observations to the HH jets. 相似文献
3.
The combination of accretion disks and supersonic jets is used to model many active astrophysical objects, viz., young stars, relativistic stars, and active galactic nuclei. However, existing theories on the physical processes by which these structures transfer angular momentum and energy from disks to jets through viscous or magnetic torques are still relatively approximate. Global stationary solutions do not permit understanding the formation and stability of these structures; and global numerical simulations that include both the disk and jet physics are often limited to relatively short time scales and astrophysically out-of-range values of viscosity and resistivity parameters that are instead crucial to defining the coupling of the inflow/outflow dynamics. Along these lines we discuss self-consistent time-dependent simulations of the launching of supersonic jets by magnetized accretion disks, using high resolution numerical techniques. We shall concentrate on the effects of the disk physical parameters, and discuss under which conditions steady state solutions of the type proposed in the self-similar models of Blandford and Payne can be reached and maintained in a self-consistent nonlinear stationary state. 相似文献
4.
We present a dynamo mechanism arising from the presence of barotropically unstable zonal jet currents in a rotating spherical shell. The shear instability of the zonal flow develops in the form of a global Rossby mode, whose azimuthal wavenumber depends on the width of the zonal jets. We obtain self-sustained magnetic fields at magnetic Reynolds numbers greater than 103. We show that the propagation of the Rossby waves is crucial for dynamo action. The amplitude of the axisymmetric poloidal magnetic field depends on the wavenumber of the Rossby mode, and hence on the width of the zonal jets. We discuss the plausibility of this dynamo mechanism for generating the magnetic field of the giant planets. Our results suggest a possible link between the topology of the magnetic field and the profile of the zonal winds observed at the surface of the giant planets. For narrow Jupiter-like jets, the poloidal magnetic field is dominated by an axial dipole whereas for wide Neptune-like jets, the axisymmetric poloidal field is weak. 相似文献
5.
The theory that magnetic fields are instrumental in the formation and propagation of jets in active galactic nuclei dates
back four decades. Despite a recent growing consensus on this notion stemming from the results of numerical simulations of
magnetohydrodynamic (MHD) flows near black holes, the precise dynamical role of magnetic fields in observed parsec and kiloparsec
jets remains uncertain. Some of the unanswered fundamental questions about extragalactic jets include the location where the
flow becomes relativistic and where acceleration and collimation terminate, as well as the specifics of how the flow interacts
with the ISM. Such observed properties as superluminal motions and wiggled structures based on numerical simulations to constitute
the foundation of an MHD paradigm for extragalactic jets. We particularly focus our attention to the M87 jet, which is one
of the best candidates to investigate relativistic outflows in extragalactic system. 相似文献
6.
自从人们获得河外射电源的第一个结构图像以来，３０多年时间已经过去了。在这段时间的后半期，人们对许多源中的喷流状结构作了大量研究。目前，我们正在分析所获得的有关喷流的第一代结果。这包括高分辨率观测，数值模拟和理论研究等诸方面的成就。在本文 详细地讨论河外射电源中的喷流。 相似文献
7.
赫比格－哈罗天体（ＨＨ天体）包含了有关原恒星吸积和抛射过程的许多重要信息,ＨＨ天体高分辨观测研究取得了一系列新进展：分辨出激波峰面、马赫盘和辐射冷却区;分辨出喷流节点的结构,发现它们大多是内工作面,而不是由Ｋｅｌｖｉｎ－Ｈｅｌｍｈｏｌｔｚ不稳定性所产生的斜激波;发现喷流宽度随到激发源距离的减小仅缓慢减小,对喷流的准直和加速模型提供了限制条件;ＨＨ天体在小尺度上尚有复杂的激发结构。对这些进展进行了评 相似文献
8.
D. M. Worrall 《Astronomy and Astrophysics Review》2009,17(1):1-46
Jet physics is again flourishing as a result of Chandra’s ability to resolve high-energy emission from the radio-emitting structures of active galaxies and separate it from the X-ray-emitting thermal environments of the jets. These enhanced capabilities have coincided with an increasing interest in the link between the growth of super-massive black holes and galaxies, and an appreciation of the likely importance of jets in feedback processes. I review the progress that has been made using Chandra and XMM-Newton observations of jets and the medium in which they propagate, addressing several important questions, including: Are the radio structures in a state of minimum energy? Do powerful large-scale jets have fast spinal speeds? What keeps jets collimated? Where and how does particle acceleration occur? What is jet plasma made of? What does X-ray emission tell us about the dynamics and energetics of radio plasma/gas interactions? Is a jet’s fate determined by the central engine? 相似文献
9.
This paper reviews the numerical simulations of radiative jets with concrete predictions of the emitted radiation, which can be compared directly with observations of individual HH objects. The only models that have been developed to this point are the “internal working surface model” (in which the structures along HH jets are interpreted as working surfaces resulting from a time-variability in the ejection) or the “Kelvin-Helmholtz instability model” (in which the HH knots are associated with shocks resulting from K-H instabilities in the jet beam/environment boundary). The predictions of intensity maps, line ratios, line profiles and proper motions are discussed. 相似文献
10.
The banded structures observed on the surfaces of the gas giants are associated with strong zonal winds alternating in direction with latitude. We use three-dimensional numerical simulations of compressible convection in the anelastic approximation to explore the properties of zonal winds in rapidly rotating spherical shells. Since the model is restricted to the electrically insulating outer envelope, we therefore neglect magnetic effects.A systematic parametric study for various density scaleheights and Rayleigh numbers allows to explore the dependence of convection and zonal jets on these parameters and to derive scaling laws.While the density stratification affects the local flow amplitude and the convective scales, global quantities and zonal jets properties remain fairly independent of the density stratification. The zonal jets are maintained by Reynolds stresses, which rely on the correlation between zonal and cylindrically radial flow components. The gradual loss of this correlation with increasing supercriticality hampers all our simulations and explains why the additional compressional source of vorticity hardly affects zonal flows.All these common features may explain why previous Boussinesq models were already successful in reproducing the morphology of zonal jets in gas giants. 相似文献
11.
Maxim G. Ponomarjov 《Astrophysics and Space Science》2000,274(1-2):423-429
In this paper a method is concerned which makes it possible to describe numerically and analytically the most famous structures
in the non-equilibrium ionosphere, such as stratified and yacht sail like structures, flute jets, wakes and clouds. These
problems are of practical interest in space sciences, astrophysics and in turbulence theory, and also of fundamental interest
since they enable one to concentrate on the effects of the ambient electric and magnetic fields. Disturbances of charged particle
flows due to the ambient flow interactions with bodies are simulated with taking into account the ambient magnetic field effect.
The effects of interactions between solid surfaces and the flows was simulated by making use of an original image method.
The flow disturbances were described by the Boltzmann equation. In the case of the ambient homogeneous magnetic field the
Boltzmann equation is solved analytically. The case of diffuse reflection of particles by surface is considered in detail.
The disturbances of charged particle concentration are calculated in 3D space. The contours of constant particle concentration
obtained from numerical simulations illustrate the dynamics of developing stratifications and flute structures in charged
particle jets and feffect. The wakes under the ambient magnetic field effect. The basic goal of this paper is to present the
method and to demonstate its possibility for simulations of turbulence, plasma jets, wakes and clouds inthe ionosphere and
Space when effects of electric and magnetic fields are taken into account.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
We study the kinds of distorted radio structures likely to be produced by the combination of slingshot mechanism, galaxy rotation, and nonradial gas flows. Since all deviations from simple radial symmetry must in the slingshot scenario be produced by passive motion of the thermally confined synchrotron emitting plasma, the dynamics of the ambient medium together with the radial motion of the ejected black holes completely determine the overall structure and evolution of the radio lobes and jets. Numerical calculations show that many commonly observed basic morphological types result naturally from the assumed mechanism. In particular, very nonsymmetric, strongly-bent sources, small sources with Z-symmetry, and jets which are initially straight and then bend suddenly over large angles, are common. Passive bending may also became important in beam models, resulting in strong distortions of the jets and lobes. 相似文献
13.
14.
Stéphane Corbel 《Astrophysics and Space Science》2005,300(1-3):275-281
Relativistic jets are now believed to be a fairly ubiquitous property of accreting compact objects, and are intimately coupled
with the accretion history. Associated with rapid changes in the accretion states of the binary systems, ejections of relativistic
plasma can be observed at radio frequencies on timescale of weeks before becoming undetectable. However, recent observations
point to long-term effects of these ejecta on the interstellar medium with the formation of large-scale relativistic jets
around binary systems. In this paper, we review the observations of these large-scale structures in microquasars, highlighting
their contributions at high energies. 相似文献
15.
Roger Blandford 《Astrophysics and Space Science》2003,288(1-2):155-160
An electromagnetic model of relativistic jets is outlined. It is suggested that these jets be interpreted as current flows and that they owe their persistence and collimation to the pinching action of the magnetic field. Such structures are unstable and it is suggested that the nonlinear development of these instabilities involves the formation of an electromagnetic turbulence spectrum. This turbulence may be responsible for the acceleration of relativistic electrons and positrons. It may also provide the electromagnetic field in which these electrons and positrons radiate. Some mechanisms through which circular polarisation may be created in this environment are outlined. 相似文献
16.
M. Birkinshaw 《Astrophysics and Space Science》1996,242(1-2):17-91
The observed properties of astrophysical jets are reviewed, and the techniques used to estimate the parameters of the underlying beams are described. This information is then used in a theoretical treatement of the Kelvin-Helmholtz instability of the flows, and the relevance of this instability to the persistence of the observed structures is emphasised. 相似文献
17.
C. D. Gregory J. Howe B. Loupias S. Myers M. M. Notley Y. Sakawa A. Oya R. Kodama M. Koenig E. Falize S. Bouquet C. Michaut N. C. Woolsey 《Astrophysics and Space Science》2009,322(1-4):37-41
We present the results of experiments in which jets are created through the collision of two laser-produced plasmas. These experiments use a simple ‘v-foil’ target design: two thin foils are placed at an angle of 140° to each other, and irradiated with a high-energy laser. The plasmas from the rear face of these foils collide and drive plasma jets moving with a velocity of ～300 km?s?1. By choosing the foil thickness and material to suit the laser conditions available, it has proven possible to create plasma jets for which the relevant scaling parameters show significant overlap with those of outflows associated with young stellar objects (YSOs). Preliminary results are also shown from experiments to study the effect of an ambient gas on jet propagation. Nominally identical experiments are conducted either in vacuum or in an ambient medium of 5 mbar of nitrogen gas. The gas is seen to increase the jet collimation, and to introduce shock structures at the head of the outflow. 相似文献
18.
Sébastien Charnoz 《Icarus》2009,201(1):191-197
Since 2004, observations of Saturn's F-ring have revealed that the ring's core is surrounded by structures with radial scales of hundreds of kilometers, called “spirals” and “jets.” Gravitational scattering by nearby moons was suggested as a potential production mechanism; however, it remained doubtful because a population of Prometheus-mass moons is needed and, obviously, such a population does not exist in the F-ring region. We investigate here another mechanism: dissipative physical collisions of kilometer-size moonlets (or clumps) with the F-ring core. We show that it is a viable and efficient mechanism for producing spirals and jets, provided that massive moonlets are embedded in the F-ring core and that they are impacted by loose clumps orbiting in the F-ring region, which could be consistent with recent data from ISS, VIMS and UVIS. We show also that coefficients of restitution as low as ∼0.1 are needed to reproduce the radial extent of spirals and jets, suggesting that collisions are very dissipative in the F-ring region. In conclusion, spirals and jets would be the direct manifestation the ongoing collisional activity of the F-ring region. 相似文献
19.
I. I. Pronik 《Astrophysics》1997,40(1):10-15
The position angles (PA) of the elongated structure of the compact source 3C84 are compared with those of the E polarization
vector of its 2, 4, and 6-cm emission. It is shown that during 1972–1984, the E vector had two preferred directions with PA
= -10° and PA = +17°, which correspond to the directions of the two principal elongated structures of the radio source, which
contain moderately relativistic subparsec-scale jets. The parallel directions of the polarization vector and radio jets for
the source 3C84 agree with the model of magnetic field and relativistic electron cloud distributions in the moderately relativistic
jets of the BL Lac objects examined by Grabusda et al. (1994).
Translated fromAstrofizika, Vol. 40, No. 1, pp. 19–28, February, 1997 相似文献
20.
Francesca Bacciotti Thomas P. Ray Jochen Eislöffel Jens Woitas Josef Solf Reinhard Mundt Christopher J. Davis 《Astrophysics and Space Science》2003,287(1-4):3-13
Collimated jets are believed to be an essential ingredient of the star formation process, and we are now able for the first time to test observationally the theories for their formation and propagation. The major advances achieved in recent years are reviewed, regarding the observed morphology, kinematics and excitation properties of jets, from the parsec-scale `giant outflows' down to the `microjets' from T Tauri stars. High angular resolution images and spectra have provided valuable estimates of jet diameter, space velocity, temperature, ionization fraction, electron and total density, both along and across the flow. We can thus calculate key physical quantites, as the shock excitation parameters, or the mass and momentum fluxes in the flow. The results obtained appear to validate the popular magneto-centrifugal models for jet launching, although some important issues are still under debate, as to the cause of knotty structures, observed wind thermal properties, and the dynamical relationship between jets and molecular outflows. Among the most interesting recent findings, we mention the observed indications for jet rotation, with inferred toroidal velocities consistent with the prescribed angular momentum balance between infall and outflow. 相似文献