Research

Large Scale Universe and the Cosmic Microwave Background (CMB)

1. CMB vs voids

The Kolmogorov stochasticity parameter, the K-statistic and other descriptors are used to reveal the voids via the temperature anomalies of the CMB maps. The Kolmogorov map technique is shown to not only enables one to study the large scale filaments from a new viewpoint but also can be a tool to separate various signals, both of cosmological and non-cosmological origin. A criterion indicating the domination of voids in the line-of-sight direction has been derived, to indicate the hyperbolicity of the photon beams while passing the voids. The temperature independent ellipticity of excursion sets measured for the CMB maps would then indicate the void hyperbolicity, described by a porosity parameter. The void induced hyperbolicity is studied vs the redshift dependence of the void size and cumulative image distortion parameter is obtained for the case of a sequence of variable size voids and given underdensity parameters, and compared to those of redshift distortion revealed in the galactic surveys.

2. The Cold Spot and Kolmogorov analysis

The structure of the Cold Spot was studied using the data by Planck satellite. The map obtained of the degree of stochasticity (Kolmogorov-map) of CMB for the cold spot, reveals, most clearly in 100 GHz band, a shell-type structure with a center coinciding with the minima of the temperature distribution. The shell structure is non-Gaussian at a 4σ confidence level. Such behavior of the K-map supports the void nature of the cold spot. Soon after our analysis the void nature of the Cold Spot has been supported by independent galaxy survey studies.
 
High redshift Hubble diagram

The data of the high redshift supernovae and gamma-ray bursters enable one the construction of the Hubble diagram sensitive to various dark energy models. The latter is particularly useful for the determination of the critical redshift value when the dark energy had started to dominate over the matter density. The observational aspects of the value of dark energy density from quantum vacuum fluctuations model for dark energy were applied to construct the Hubble diagram for those classes of observational samples, supernova and gamma bursters, showing that this approach provides viable predictions for distances up to redshift around 9.
 
Galaxy clusters and galactic dark halos

The detection of clusters of galaxies in large surveys plays an important part in extragalactic astronomy, and particularly in cosmology, since cluster counts can give strong constraints on cosmological parameters. X-ray imaging is in particular a reliable means to discover new clusters, and large X-ray surveys are now available. Considering XMM-Newton satellite data for a sample of 40 Abell clusters, we showed that their analysis with a Kolmogorov distribution can provide a distinctive signature for galaxy clusters. The Kolmogorov technique is sensitive to the correlations in the cluster X-ray properties and can therefore be used for their identification, thus allowing to search reliably for clusters in a simple way.

We have studied the microwave data obtained by the WMAP and Planck satellites to trace the dark halos of a sample of spiral galaxies, M31, M82, M104, M33. We detected a temperature asymmetry in the halos for several microwave bands along the rotation direction which thus can open a way to probe hidden baryons in galactic dark halos using high accuracy microwave measurements of nearby edge-on spiral galaxies.
 
Lambda-gravity, the Hubble tension and absolute constraints on the local Hubble parameter

The Lambda-gravity, i.e. a modified weak-field General Relativity is shown to describe the dynamics of galaxy groups and clusters, as well as the Hubble tension as result of two flows, local and global ones. That modification follows from a theorem on the general function satisfying the identity of sphere’s gravity and that of a point situated in its center. It is shown that, although similar, the Newtonian and Friedmann–Lemaître–Robertson–Walker (FLRW) set of equations have a principal difference and enable to define two flows, local and global ones, thus naturally exposing the Hubble tension at the presence of the cosmological constant. Absolute constraints are obtained for the lower and upper values for the local Hubble parameter. The link to the so-called maximum force–tension issue in cosmological models is revealed. Certain consequences for consideration of the cosmological constant as a universal constant are revealed.
 
Supernovae and their host galaxies

A detailed examination of the spatial distribution of supernovae within their host galaxies provides a unique avenue to unveil distinct explosion mechanisms and constrain the progenitor natures. Specifically, Type Ia supernovae are believed to be the evolutionary endpoint, accompanied by the thermonuclear explosion, of carbon-oxygen white dwarf stars in interacting close binary systems. These events play a key role in understanding the evolution of binary stellar systems, the chemical enrichment of galaxies, and the nature of accelerating expansion of the Universe. By scrutinizing correlations among observational parameters such as supernova luminosities, the expansion velocity of their ejecta, spectroscopy, and host galaxy properties like star formation rates, metallicities, dynamical features, and stellar population ages, it is possible to discern between single-degenerate and double-degenerate explosion scenarios, both of which may probably occur in nature.

 
Artificial Intelligence algorithms and data analysis

Machine Learning approach to detect and extract information from the astronomical datasets on the shapes of such objects as galaxies, star clusters and of the gravitational lenses, has been developed. First, the Kolmogorov stochasticity parameter was used to retrieve the sub-regions that are worth further attention, then the image processing and machine learning Principal Component Analysis algorithm to retrieve the sought objects and reveal the information on their morphologies was applied. The results show the capability of the approach to identify distinct objects and to classify them based on the input parameters.

The dynamics of S-stars in the Galactic center was studied using the physics-informed neural networks. For both, Keplerian and the General Relativity dynamics, the orbital parameters for a sample of S-stars were obtained and the regression problem was solved. The results revealed the efficiency of the physics-informed neural networks (PINN) neural network in detecting the Schwarzschild precession for S2 star and constraining the General Relativity and modified gravity theories.

     
 
Complex systems

1. Dynamical chaos

The geometrical i.e. of  Maupertuis parametrization, stochastic differential equation (of Van Kampen type)  approaches is used to continue the study of chaotic properties of gravitating systems. The technique has probed with the results of parallel numerical simulations of N-body systems. The results then will be applied to the observational data on star clusters and elliptical galaxies.

2. Composite signals

The technique of degree of randomness is used to model the correlations in sequences containing various subsignals and noise. Kolmogorov stochasticity parameter enables to quantify the randomness in number sequences and hence appears as an efficient tool to distinguish the signals. Numerical experiments for a broad class of composite signals of regular and random properties enable to obtain the qualitative and quantitative criteria for the behavior of the descriptor depending on the input parameters typical to astrophysical signals.
 
A new limit on the light speed isotropy from the GRAAL experiment at the European Synchrotron Radiation Facility (Grenoble)

When the electrons stored in the ring of the European Synchrotron Radiation Facility (ESRF) scatter on a laser beam, the lower energy of the scattered electron spectra, the Compton Edge (CE), is given by the two body photon-electron relativistic kinematics and depends on the velocity of light. A precision measurement of the position of this CE as a function of the daily variations of the direction of the electron beam in an absolute reference frame of the cosmic microwave background provides a one-way test of relativistic kinematics and the isotropy of the velocity of light, as was originally suggested by Gurzadyan and Margarian (1996). The results of GRAAL-ESRF measurements improve the previously existing one-way limits, up to 10^-14, thus showing the efficiency of this method and the interest of further studies in this direction.
 
Testing General Relativity: participation in LARES satellite project

The recently launched LAser RElativity Satellite (LARES) is expected to provide high precision constraints to the General Relativity, the frame dragging Lense-Thirring effect, as well as to the extensions of General Relativity such as the Chern-Simons gravity with metric coupled to a scalar field.

The correspondence between geodesic motion in General Relativity and the motion of an extended body by means of the Ehlers-Geroch theorem was studied in the context of LARES. It was shown that being possibly the highest mean density orbiting body in the Solar system, LARES provides the best realization of a test particle ever reached experimentally and provides a unique possibility for testing the predictions of General Relativity.

The Kolmogorov analysis of the residual data of two LAGEOS satellites on General Relativistic Lense-Thirring effect reveals a tiny difference in the properties of the satellites, explained by Yarkovsky-Rubincam effect of thermal thrust. This is the first detection of the latter effect for artificial satellites.