[en] This paper reveals evidence that while primordial binaries are common in Pop I fields, to about the 50% level, they may also occur in globular clusters at the 25% level common to Pop II fields. (UK)

[en] A simple explanation of the tidal distortion of a solar-system body from the differential gravitational attraction by an orbiting companion is given. This is followed by an explanation of how energy dissipation caused by time variations in the tidal bulge leads to changes in the orbits and spins that can be large over the age of the solar system. Consequences of this orbital and spin evolution are pointed out for all solar-system bodies for which the effects of tidal dissipation are significant. 13 references

[en] The membrane formalism is applied to various types of gravitational perturbations of a black hole. Attention is given to the disturbance of the horizon of a black hole by compact masses lowered toward a nonrotating hole and the deformations experienced by a rotating hole. Nonaxisymmetric gravitational tidal fields in rigid motion about a rotating hole are considered, along with the behavior of massive particle moving along the equator of a rotating hole, and the spindown of a rotating hole in an external tidal field. The extraction of rotational energy from a black hole by orbiting bodies is examined, as are superradiant scattering of gravitational waves and the quasi-normal modes of a black hole. The perturbations imparted to a black hole by a compact body plunging into the membrane (a stretched horizon) at a velocity close to the local light speed and by a radially accelerated particle above the horizon of a nonrotating hole are also explored

[en] Tunneling processes leading to the decay of the false vacuum are studied in the theory of a scalar field interacting with gravity. It is shown that in the theory with conformal coupling [the action containing the term (1/12)Rphi²] bubbles with wormhole geometry can be produced, whereas this is impossible in the theory with minimal coupling

[en] This paper considers the collisional relaxation of an electrostatic plasma and a gravitationally interacting system in the context of a homogeneous expanding universe. For an electrostatic plasma, one anticipates, in the absence of an expansion, a relaxation towards a Maxwellian distribution of velocities on a time scale t/sub R/. If, however, one allows for an expansion, working in the average comoving frame, one anticipates instead deviations from a Maxwellian distribution. Provided that the Debye time scale t/sub D/ is small compared with the expansion time t/sub E/, one anticipates that these deviations will be manifest on a time scale t/sub S/approx.(t/sub E//t/sub D/) ln (t/sub D//t/sub C/)t/sub R/>>t/sub R/, where t/sub C/<< t/sub D/ is the characteristic time scale associated with close encounters, in which a linear-trajectory approximation fails. For the case of gravitational interactions, which are themselves responsible for the overall expansion, there again exist time scales t/sub S/ and t/sub R/. In this case, however, t/sub S/approx.ln(t/sub asterisk//t/sub C/)t/sub R/, where t/sub asterisk/equivalentmin(t/sub E/,t/sub R/). .AE

[en] An analytic formalism is developed to predict the cumulative effects of tidal encounters on disc galaxies in a variety of environments. The starting point is a modification of the standard impulse approximation that softens the interactions of overlapping galaxies. This is used to compute the changes in the stellar velocities parallel and perpendicular to the plane of a target disc during a single collision. A 20 000-body simulation shows that the corresponding energy changes are amplified only slightly by collective effects if the disc is stabilized by a halo. With this provision, the kinematic formulae is used with averaging over a realistic distribution of perturber masses and velocities. This excludes merging and adiabatic encounters but it includes gravitational focusing and a proper weighting of the density profile in an aggregate. The results show that most of the tidal heating is caused by interpenetrating collisions with velocities a few times higher than the circular velocities of the discs. The predicted changes in the epicyclic and vertical energies are then compared with observational data for a sample of galaxies in nearby groups and the Virgo cluster. (author)

[en] Numerical simulations of merging galaxies do not include a disc component due to bar instability modes. Analytic work is based upon the impulsive approximation which leads to energy loss by the perturber. However, for the perturber to become bound we need consider parabolic encounters. Here, the author presents an analytic technique suitable for all types of encounters. (orig.)

[en] A series of disc galaxy models are constructed and their deformation in the tidal interaction is investigated by N-body simulations. Each galaxy model is composed of a self-gravitating disc made up of many particles and a rigid halo component added to stabilize the disc. Each model is characterized by two parameters; the mass fraction of the disc and the mass concentration of the halo toward the centre. These parameters are widely varied to investigate the dependence on internal structure whereas the relative motions of two galaxies are restricted to parabolic prograde planar encounters. It is found that the self-gravitating discs, when perturbed by the tidal force of another galaxy, develop prominent spiral structures not only in the outer region but also in the inner region. This is a remarkable contrast to the case of the massless discs constructed by test particles, in which only the outer part exhibits a spiral structure. (author)

[en] The results are given of detailed UBV photometry of the peculiar galaxy NGC 2685 based on 10 negatives obtained with the 2.6-m telescope of the Biurakan Observatory. Consideration of all the available observational data (photometric, spectroscopic, and polarization) suggests that NGC 2685 is a pair of colliding galaxies. 18 references

[en] The structural properties of the dwarf spheroidal satellite galaxies of the Milky Way may be strongly affected by their time-dependent interactions with the tidal field of the Milky Way. A low Q resonance of the tidal driving force with collective oscillation modes of the dwarf system can produce many of the observed properties of the Local Group dwarf spheroidal galaxies, including large velocity dispersions that would normally be interpreted as indicating large dynamical masses. 18 refs