Neutralino Stars Research Articles

Astrophysics: Macroobject Shell Model

The model proposes that Nuclei of all macroobjects (Galaxy clusters, Galaxies, Star clusters, Extrasolar systems) are made up of Dark Matter Particles (DMP). These Nuclei are surrounded by Shells composed of both Dark and Baryonic matter. This model is used to explain various astrophysical phenomena: Multi-wavelength Pulsars; Binary Millisecond Pulsars; Gamma-Ray Bursts; Fast Radio Bursts; Young Stellar Object Dippers; Starburst Galaxies; Gravitational Waves. New types of Fermi Compact Stars made of DMP are introduced: Neutralino star, WIMP star, and DIRAC star. Gamma-Ray Pulsars are rotating Neutralino and WIMP stars. Merger of binary DIRAC stars can be a source of Gravitational waves.

Equation of State for Neutralino Star as a Form of Cold Dark Matter

In order to study the structure of neutralino star and dark galaxy, we consider dynamical interactions due to boson-exchange in the neutralino matter. Taking into account interactions of neutralinos with bosons, we derive the equation of state (EOS) of neutralino stars in terms of the relativistic mean-field approach. Then we apply the resulting EOS to investigate properties of the neutralino star such as its density profile and mass limit. For example, if the neutralino mass is around 1 TeV, the Oppenheimer mass limit of the neutralino star is obtained as 6.06 × 10−7M⊙, and the corresponding radius is about 7.8 mm. Actually, due to an increasing annihilation rate as indicated by our calculation, this dense state can never be realized in practice. Our results also show that the low-density neutralino star may be a possible aggregation of the cold dark matter.

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.

Interaction between black holes and dark matter

If dark matter consists of neutrinos and antineutrinos or neutralinos then they may annihilate and radiate x rays. This fermionic matter in galactic nuclei may be very dense. Black holes assumed to be at the center of such neutrino or neutralino stars can engulf the matter permanently. Observable signs and the time evolution of such a system are studied in this paper.

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.

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.

Gamma radiation by neutralino stars

A new model of gamma radiation (GR) generated by neutralino annihilation in neutralino stars (NeS) is proposed. Diffuse galactic and extragalactic GR is calculated for this model and is shown to be in reasonable agreement with observations. The point-source component (P) is picked out among nonidentified discrete gamma sources from the EGRET catalog. This component is shown to be distributed isotropically and homogeneously, as it should be for NeS. Gamma radiation from a significant part of P-sources is supposed to be the direct radiation from individual NeS. This supposition is shown to be in agreement with observations. The comparison of the theory with observed GR gives a possibility to establish some important features of the CDM particle.

On neutralino stars as microlensing objects

The microlensing objects, Machos, recently observed in the halo of our Galaxy, can be interpreted as dense neutralino objects, neutralino stars, produced by the gravitational instability of neutralino ggas. Taking the mass and radius of these objects from microlensing observations we calculated the diffuse gamma-ray flux produced in neutralino-neutralino annihilation inside the objects. The resulting flux is many orders of magnitude higher than the observed one.

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.

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 .