Drifting through the medium: kicks and self-propulsion of binaries within accretion discs and other environments

ABSTRACT Compact binaries are within the reach of gravitational and electromagnetic wave detectors, and are important for our understanding of astrophysical environments and the composition of compact objects. There is a vast body of work devoted to the evolution of such binaries in background media, such as in common-envelope evolution, accretion discs and dark matter mini spikes. Here, we explore further gravitationally bound binaries evolving within an environment. We show that dissipative effects such as gravitational drag and accretion impart a momentum to the centre of mass (CM) of asymmetric binaries. We numerically evolve the binaries in a Newtonian setup and show that, depending on the medium density, the CM can accelerate to high speeds – in some cases $300\, {\rm km\, s^{-1}}$ or more – during inspiral, with potentially observable signatures. Our numerical results are fully consistent with an analytical result for the CM evolution at first order in the medium density.

Cosmological constant in coherent quantum gravity

It is argued that quantum states of geometry, like those of particles, should be coherent on light cones of any size. An exact classical solution, the gravitational shock wave of a relativistic point particle, is used to estimate gravitational drag from coherent energy flows, and the expected gravitational effect of virtual transverse vacuum energy fluctuations on surfaces of causal diamonds. It is proposed that the appropriately spacetime-averaged gravitational effect of the Standard Model vacuum state leads to the observed small nonzero value of the cosmological constant, dominated by gravitational drag of virtual gluonic strings at the strong interaction scale.

Dynamical friction in slab geometries and accretion discs

ABSTRACT The evolution of planets, stars, and even galaxies is driven, to a large extent, by dynamical friction of gravitational origin. There is now a good understanding of the friction produced by extended media, either collisionless or fluid-like. However, the physics of accretion or protoplanetary discs, for instance, is described by slab-like geometries instead, compact in one spatial direction. Here, we find, for the first time, the gravitational wake due to a massive perturber moving through a slab-like medium, describing e.g. accretion discs with sharp transitions. We show that dynamical friction in such environments can be substantially reduced relatively to spatially extended profiles. Finally, we provide simple and accurate expressions for the gravitational drag force felt by the perturber, in both the subsonic and supersonic regime.

Injuries and vital reactions patterns in hanging

Hanging is a form of ligature strangulation in which the force applied to the neck is derived from the gravitational drag of one?s own body weight. A furrow - dessication is the most common form of ligature mark on the skin. The furrow is a postmortem phenomenon due to ligature pressure and it is more detectable as the suspension time becomes longer. Vital reaction is a phenomenon that shows if the injury was premortal. Vital signs could be present at the injury site, thus it is termed as local, but they could also be remote from the injury site, and then they are termed general vital signs. The presence and recognition of any vital reaction in each pathoforensic case indicate vitality of certain injury, which is sometimes exceptionally useful in solving the case under investigation. Although in cases of hanging there is usually no question about the vitality of injury, this does not mean that one should not recognize the type of vital reactions and location of occurrence of these phenomena in such cases. Most often they can be also useful in the reconstruction of the mechanism. This paper presents most common vital reactions in hanging, with explanation of their underlying mechanisms, and their significance in forensic pathology is pointed out.

Dynamics of Metallic Particle Contamination in Gas Insulated Substation (GIS)

This paper analyses the movement of free conducting particles inside a single phase Gas Insulated Bus duct(GIB).A two dimensional mathematical model was proposed for determining the movement pattern of metallic particle in GIB by considering all the forces acting on the particle like gravitational, drag and the electric field forces. These particles may be free to move in the electric field or may be fixed on the conductors, thus enhancing local surface fields. Electric fields at the instantaneous contaminated particle locations were computed using Charge Simulation Method (CSM).To determine the particle trajectory in a single phase Gas Insulated Bus duct (GIB), an enclosure diameter 152 mm and conductor diameter 55 mm is considered. The simulation of the particle movement was carried under different AC voltage levels like 100KV, 132KV, 145KV and 175KV class enclosure of GIB for aluminum, copper and silver particles. The results of the simulation have been presented and analyzed in this paper.