SZ effect from radio-galaxy lobes: astrophysical and cosmological relevance

We derive the Sunyaev–Zel'dovich (SZ) effect arising in radio-galaxy lobes that are filled with high-energy, non-thermal electrons. We provide here quantitative estimates for SZ effect expected from the radio-galaxy lobes by normalizing it to the inverse Compton light, observed in the X-ray band, as produced by the extrapolation to low energies of the radio emitting electron spectrum in these radio lobes. We compute the spectral and spatial characteristics of the SZ effect associated to the radio lobes of two distant radio galaxies (3C 294 and 3C 432) recently observed by Chandra , and we further discuss its detectability with the next generation microwave and submm experiments with arcsec and ∼μK sensitivity. We finally highlight the potential use of the SZ effect from radio-galaxy lobes in the astrophysical and cosmological context.     

Instabilities in astrophysical jets

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.     

Vorticity and astrophysical magnetism

Viscous resistance to differential rotation causes a current whose magnetic field is proportional to the vorticity of the medium. The magnetic fields of stars and galaxies could arise in this manner, provided that the time scale for development of the field is reasonable. The latter condition (assuming Ohmic rather than synchroton dissipation) requires that the scale length for a galactic field be less than 3×10¹³ cm. It is suggested that there may be continual generation of field within the core of a vortex of this dimension in the galactic nucleus, the field lines then being carried outwards by expanding plasma. The main observational evidence in connection with solar, stellar and galactic magnetic fields is appraised in the context of the above theory.     

Ion contribution to the astrophysical important 388.86, 471.32 and 501.56 nm He I spectral lines broadening

Characteristics of the astrophysical important Stark broadened 388.86 nm, 471.32 nm and 501.56 nm He I spectral line profiles have been measured at electron densities between 4.4·10²² and 8.2·10²² m⁻³ and electron temperatures between 18,000 and 33,000 K in plasmas created in five various discharge conditions using a linear, low-pressure, pulsed arc as an optically thin and reproductive plasma source operated in a helium–nitrogen–oxygen gas mixture. On the basis of the observed asymmetry of the line profiles, we have obtained their ion broadening parameters (A) caused by influence of the ion microfield and also the influence of the ion dynamic effect (D) to the line shape. Our A and D parameters represent the first data obtained experimentally by the use of the line profile deconvolution procedure. We have found stronger influence of the ion contribution to these He I line profiles than the semiclassical theoretical approximation provides. This can be important for some astrophysical plasma modelling or for diagnostics.     

Electron impact broadening of multicharged ion lines of astrophysical interest: Ne VII,Ne VIII and Si XI

The modified semi-empirical method, often used in the investigations of stellar plasma for the determination of needed Stark line widths, is adapted here to use more accurate collision strengths instead of Gaunt factor. It is demonstrated that in such a way its applicability is extended to highly charged ions and good agreement is obtained with the more sophisticated semi-classical perturbation approach up to Si XI. Using this method, Stark line widths of several complex ions: two Be-like ions (Ne VII and Si XI) and one Li-like neon (Ne VIII) were calculated. The obtained results were compared with experiments and other theoretical approaches.     

Fermi acceleration in astrophysical jets

We consider the acceleration of energetic particles by Fermi processes (i.e., diffusive shock acceleration, second order Fermi acceleration, and gradual shear acceleration) in relativistic astrophysical jets, with particular attention given to recent progress in the field of viscous shear acceleration. We analyze the associated acceleration timescales and the resulting particle distributions, and discuss the relevance of these processes for the acceleration of charged particles in the jets of AGN, GRBs and microquasars, showing that multi-component powerlaw-type particle distributions are likely to occur.     

Stability of astrophysical disks and rings

Astronomical Institute, Russian Academy of Sciences. Translated fromAstrofizika, Vol. 35, No. 1, pp. 131–149, July–August, 1991.     

Nonlinear wave-wave interactions in astrophysical and space plasmas

We discuss nonlinear mode-mode coupling phenomena in cosmic plasmas. Four problems are considered: (1) nonlinear three-wave processes in the planetary magnetosphere involving the interaction of auroral Langmuir, Alfvén and whistler waves, (2) nonlinear three-wave processes in the solar wind involving the modulation of Langmuir and electromagnetic waves by ion-acoustic waves, (3) order and chaos in nonlinear four-wave processes in cosmic plasmas, and (4) regular and chaotic dynamics of the relativistic Langmuir turbulence and its application to pulsar and AGN emissions. The observational evidence in support of nonlinear wave-wave interactions in space and astrophysical plasmas is presented.     

Numerical simulators of stability in astrophysical problems

The aim of this paper is to discuss systematically two numerical methods that can play the significant role of numerical simulators of stability in the corresponding astrophysical problems to which they are applied.     

Advances in numerical modeling of astrophysical and space plasmas

Plasma science is rich in distinguishable scales ranging from the atomic to the galactic to the meta-galactic, i.e., themesoscale. Thus plasma science has an important contribution to make in understanding the connection between microscopic and macroscopic phenomena. Plasma is a system composed of a large number of particles which interact primarily, but not exclusively, through the electromagnetic field. The problem of understanding the linkages and couplings in multi-scale processes is a frontier problem of modern science involving fields as diverse as plasma phenomena in the laboratory to galactic dynamics.Unlike the first three states of matter, plasma, often called the fourth state of matter, involves the mesoscale and its interdisciplinary founding have drawn upon various subfields of physics including engineering, astronomy, and chemistry. Basic plasma research is now posed to provide, with major developments in instrumentation and large-scale computational resources, fundamental insights into the properties of matter on scales ranging from the atomic to the galactic. In all cases, these are treated as mesoscale systems. Thus, basic plasma research, when applied to the study of astrophysical and space plasmas, recognizes that the behavior of the near-earth plasma environment may depend to some extent on the behavior of the stellar plasma, that may in turn be governed by galactic plasmas. However, unlike laboratory plasmas, astrophysical plasmas will forever be inaccessible to in situ observation. The inability to test concepts and theories of large-scale plasmas leaves only virtual testing as a means to understand the universe. Advances in in computer technology and the capability of performing physics first principles, fully three-dimensional, particle-in-cell simulations, are making virtual testing a viable alternative to verify our predictions about the far universe.The first part of this paper explores the dynamical and fluid properties of the plasma state, plasma kinetics, and the radiation emitted from plasmas. The second part of this paper outlines the formulation for the particle-in-cell simulation of astrophysical plasmas and advances in simulational techniques and algorithms, as-well-as the advances that may be expected as the computational resource grows to petaflop speed/memory capabilities.Dedicated to the memories of Hannes Alfvén and Oscar Buneman; Founders of the Subject.     

Development of force-free current in astrophysical circumstances

The physical conditions needed for the development of field-aligned force-free current in astrophysical circumstances are considered. It is shown that a large-scale differential motion of magnetic regions can lead to the development of magnetic field with the preferential enhancement of force-free current. Other physical consequences of force-free current in evolving magnetic field are also discussed.     

Launching mechanisms of astrophysical jets

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.     

Collimation of astrophysical MHD outflows

We explain in simple terms why a rotating and magnetized outflow forms a core with a jet and show numerical simulations which substantiate this argument. The outflow from a solar-type inefficient magnetic rotator is found to be very weakly collimated while the outflow from a ten times faster rotating YSO is shown to produce a tightly collimated jet. This gives rise to an evolutionary scenario for stellar outflows. We also propose a two-component model consisting of a wind outflow from a central object and a faster rotating outflow launched from a surrounding accretion disk which plays the role of the flow collimator.     

Electron runaway in turbulent astrophysical plasmas

An astrophysical electron acceleration process is described which involves turbulent plasma effects: the acceleration mechanism will operate in ‘collision free’ magnetoactive astrophysical plasmas when ion-acoustic turbulence is generated by an electric field which acts parallel to the ambient magnetic lines of force. The role of ‘anomalous’ (ion-sound) resistivity is crucial in maintaining the parallel electric field. It is shown that, in spite of the turbulence, a small fraction of the electron population can accelerate freely, i.e. runaway, in the high parallel electric potential. The number density n^(B) of the runaway electron component is of order $\text{n}{}^{\mathrm{(B)}}\text{?}\text{n}\text{2}\text{(}\text{c}{}_{\mathrm{s}}\text{U}{}_{\mathrm{\parallel }}{}^{\mathrm{?}}\text{)}{}^2$, where n = background electron number density, c_s = ion-sound speed and U_∥^? = relative drift velocity between the electron and ion populations. The runaway mechanism and the number density n^(B) do not depend critically on the details of the non-linear saturation of the ion-sound instability.     

Cosmological and astrophysical neutrino mass measurements

Cosmological and astrophysical measurements provide powerful constraints on neutrino masses complementary to those from accelerators and reactors. Here we provide a guide to these different probes, for each explaining its physical basis, underlying assumptions, current and future reach.     

The Balmer jump in astrophysical hydrogen plasmas

It is shown that, according to accepted theoretical concepts, there should be no intensity jump at the edge of the Balmer continuum, nor at that of other hydrogen series. We point out three reasons for a fairly smooth increase of the intensity to occur at the continuum edge. As a result, the jump sometimes spreads over hundreds of ångstroms, due mainly to the electron density inhomogeneity of solar plasma. Furthermore, the Doppler and Stark effects also give rise to a considerable spread of the series edge. We point out that excess continuum emission over a relatively narrow spectral interval before the continuum edge can result from overlapping of line wings.