Noncompact Objects Research Articles

On the origin of the lump in circumbinary discs

ABSTRACT Accreting binary black holes (BBHs) are multimessenger sources, emitting copious electromagnetic (EM) and gravitational waves. One of their most promising EM signatures is the light-curve modulation caused by a strong unique and extended azimuthal overdensity structure orbiting at the inner edge of the circumbinary disc (CBD), dubbed ‘lump’. In this paper, we investigate the origin of this structure using 2D general-relativistic (GR) hydrodynamical simulations of a CBD in an approximate BBH space–time. First, we use the symmetric mass-ratio case to study the transition from the natural m = 2 mode to m = 1. The asymmetry with respect to m = 2 grows exponentially, pointing to an instability origin. We indeed find that the CBD edge is prone to a (magneto)hydrodynamical instability owing to the disc edge density sharpness: the Rossby Wave Instability (RWI). The RWI criterion is naturally fulfilled at the CBD edge and we report the presence of vortices, which are typical structures of the RWI. The RWI is also at work in the asymmetric mass-ratio cases (from 0.1 to 0.5). However, the CBD edge sharpness decreases with a decreasing mass ratio, and so the lump. By proposing a scenario for this lump formation, our work further supports its existence in astrophysical CBDs and potential source for an EM signature of BBHs. Finally, because the RWI is not caused by GR effects, it is also a robust candidate for the lump origin in CBDs around non-compact objects, e.g. binary protostars.

Generalized tensor idempotents and the telescope conjecture

We transpose Rickard's construction of idempotent representations to the general context of tensor triangulated categories. We connect our construction to the telescope conjecture and prove that the latter is of local nature. As an illustration, we extend the affine telescope theorem of Neeman to arbitrary noetherian schemes. We also develop supports for non-compact objects.

A common origin of neutralino stars and supermassive black holes

To account for the microlensing events observed in the Galactic halo, Gurevich, Zybin, and Sirota have proposed a model of gravitationally bound, noncompact objects with masses of 0.01-1M_\odot. These objects are formed in the expanding Universe from adiabatic density perturbations and consist of weakly interacting particles of dark matter, for example, neutralinos. They assumed the perturbation spectrum on some small scale to have a distinct peak. We show that the existence of this peak would inevitably give rise to a large number of primordial black holes (PBHs) with masses of \sim10^5M_\odot at the radiation-dominated evolutionary stage of the Universe. Constraints on the coefficient of nonlinear contraction and on the compactness parameter of noncompact objects were derived from constraints on the PBH number density. We show that noncompact objects can serve as gravitational lenses only at a large PBH formation threshold, \delta_c > 0.5, or if noncompact objects are formed from entropic density perturbations.

13.1: Multilayer PDLC Screen for Holography and Displaying of Non‐Compact Objects

AbstractA method of writing dynamical pictures with non‐compact scenes for the purposes of information displaying or holography is described. Each section of a non‐compact scene is registered by an independent TV camera and projected onto a multilayer PDLC screen. The success of driving pulses to change the PDLC layer transparency is selected in accordance with the section number.

Possible evidence for the observation of noncompact (nonbaryonic) gravitational microlenses (“neutralino stars”)

The microlensing of distant stars by noncompact objects such as neutralino stars is considered. Recently, Gurevich and Zybin considered the objects as microlenses. Using a nonsingular density distribution, we analyze microlensing by noncompact objects. We obtain analytic solutions to the gravitational-lens equation and an analytic expression for the amplification factor of the gravitational lens. We show that, on the basis of a model of microlensing by noncompact objects, it is possible to interpret microlensing-event candidates having two typical maxima of light curves which are usually interpreted as binary microlenses.

Characteristic features of microlensing by noncompact objects of dark matter

A theory of microlensing by nonbaryonic bodies is developed. The characteristic features of lensing by noncompact transparent objects with a singular density distribution are investigated. The conditions under which additional peaks appear in the brilliance curve and the characteristics of these peaks are determined. The effect of a compact baryonic nucleus on the brilliance curve is studied.

Non-compact astronomical objects as microlenses

Abstract The microlensing of the distant stars by neutralino stars is considered. The neutralino sars have been considered in the recent paper of Gurevich and Zybin; moreover, it has been suggested that the stars should be regard as a major component of dark matter. The optics of these gravitational microlenses, namely the gravitational lens equation, its solutions, increasing of images and critical and caustic curves are analysed by using a clear approximation. The set of model parameters is considered.

Noncompact Objects as Microlenses

The first results of observations of microlensing have discovered a phenomenon, predicted in the papers of Byalko (1969) and Paczynsky (1986). A character of the gravitational microlens is unknown till now, although the most widespread hypothesis assumes that they are compact dark objects as brown dwarfs. Nevertheless, they could be presented by another objects, in particular, an existence of the dark objects consisting of the super symmetrical weakly interacting particles (neutralino) has been recently discussed in the papers of Gurevich et al. We consider microlensing by a neutralino star in framework of a rough model which is rather clear and we obtain analytical expressions for results. We approximate the density of distribution mass of a neutralino star in formwhere r is the current value of a distant from star's center, ρo is mass density of a neutralino star for distance a0 from a center, an is a “radius” neutralino star. The detailed analysis of the model is presented in the papers of Zakharov & Sazhin (1996a, 1996b). This research has been supported in part by Russian Foundation of Fundamental Research (grant N 96-02-17434).

Degenerate properties of a singular model for polarization during microlensing by non-compact objects

Recently Belokurov and Sazhin considered polarization curves during microlensing for non-compact objects. The con-cluded that the polarization curves for compact and non-compact objects demonstrated very distinguishable shapes, but light curves had similar shapes for compact and non-compact objects in those cases. We analyse their samples and show that the polarization curves coincided for compact and non-compact objects because the radii of non-compact objects are much smaller than the Einstein-Chwolson radius. If the radii of non-compact objects are much greater than the Einstein-Chwolson radius, then the differences between the polarization curves for compact and non-compact objects are connected with the singularity (degeneracy) of the isothermal sphere model, since the differences disappear in the framework of the non-singular isothermal sphere model.

Polarization during gravitational microlensing on noncompact objects

The first observations of the galactic bulge have directly confirmed the existence of the microlensing effect, but the nature of microlenses is still unknown. The most widespread hypothesis is that these objects are brown dwarfs. Recently, another very interesting hypothesis, using nonbaryonic matter as the material for the formation of dark bodies was put forward. Using this idea we consider the polarization for microlensing on a noncompact (nonbaryonic) object. The polarization curves were calculated for the models of compact (baryonic) and noncompact (nonbaryonic) lenses. The results of our calculations show a significant difference between the curves, that can be used for the identification of the object participating in the effect.

Melkomasshtabnaya struktura temnoi materii i mikrolinzirovanie

It has been revealed using microlensing that a considerable part, possibly more than half, of the dark matter in the halo of our Galaxy consists of objects with a mass spectrum ranging from 0.05 to 0.8 of the solar mass. What is the nature of these objects? There exist two hypotheses. According to one, these are Jupiter type planets or small stars (brown and white dwarfs) consisting of normal baryonic matter. According to the other, these are non-compact objects, i.e., small-scale formations in non-baryonic dark matter. Here, a theory is proposed describing the possibility of the existence of non-compact objects in the halo of our Galaxy, their structure and formation from non-baryonic matter. The theory of microlensing on compact and non-compact objects is considered in detail. The results of microlensing observations are described and compared with theory. Possible astrophysical manifestations of the presence of small-scale structure are pointed out. The field is being extensively studied and is of fundamental interest for cosmology and astrophysics.

Microlensing by noncompact objects

Microlensing of background stars by neutralino stars, which were proposed in a recent work by Gurevich and Zybin as the component making the main contribution to the dark matter, is studied. The optics of such a gravitational microlens—the equation of the lens, the solution of this equation, the intensification of images, and the critical and caustic curves—are analyzed in detail in a quite simple approximation. A set of different values of the parameters of the problem is studied.

Microlensing by non-compact halo objects

A detailed theory is developed for microlensing by non-compact dark matter objects - the neutralino stars - predicted by Gurevich and Zybin [Phys. Lett. A 208 (1995) 276]. It is shown that microlensing observations are in agreement with the theory. A method allowing one to test the presence of non-compact objects is pointed out. Among the available observational data, one case is presented where the difference between the microlensing by non-compact and compact objects is clearly seen. The size of the object determined from these observations is R x ⋍ 10 14 cm .