arXiv subjects

A. Stepanian

Publications and source records attributed to A. Stepanian.

At least 19 recordsLinked to original sources

arXiv2022

Tidal disruption effects near black holes and Lambda-gravity

The tidal disruption of stars in the vicinity of massive black holes is discussed in the context of $\Lambda$-gravity. The latter provides an explanation to the Hubble tension as a possible consequence of two Hubble flows, the local and global ones. The bunch of notions which play role for the considered tidal effect are obtained, along with the rate of the disrupted stars. The role of pulsars is emphasized due to their ability to penetrate up to the horizon of the massive black hole as for them the tidal radius can reach the horizon. Tidal disruption mechanism also can lead to segregation of stars by their mean density vs the distance from the black hole, the denser stars surviving at shorter distances. The interplay of the central gravity field and the repulsive $\Lambda$-term increasing with radius and its certain observational consequences are discussed.

gr-qc↗

arXiv2022

The cosmological constant vs adiabatic invariance

The property of adiabatic invariance is studied for the generalized potential satisfying the condition of identity of sphere's and point mass's gravity. That function contains a second term corresponding to the cosmological constant as weak-field General Relativity and enables to describe the dynamics of groups and clusters of galaxies and the Hubble tension as a result of two flows, local and global ones. Using the adiabatic invariance approach we derive the orbital parameters via Weierstrass functions, including the formula for the eccentricity which explicitly reveals the differences from the Kepler problem.

gr-qc↗

arXiv2021

On the Galactic CMB apex

The hierarchy of motions that we are participating is well known, from the Earth's motion around the Sun and Sun's motion in the Milky Way, up to the Local Group's motion within the Virgo Supercluster of galaxies. The dipole anisotropy of the Cosmic Microwave Background (CMB) enables to define Sun's motion with respect to the CMB "absolute" frame. We now present evidence for CMB Galactic dipole signal due to the Sun's motion in the Galaxy, by means of Planck 2018 data and Gaia Early Data Release 3. The signal is weak and frequency depended, the strongest is at 30 GHz, up to 7.6\sigma confidence. The amplitude of the signal interpreted as Doppler caused, corresponds to velocity $v \approx 225.5 \pm 16.2 \, km\, sec^{-1}$, in agreement with Solar system's velocity with respect to the Galactic center. While the revealing of precise coordinates of the apex will need further refined analysis at various bands, the detected weak signal can indicate the appearance of a new cosmic scaling in CMB, thus opening a link to a bunch of physical effects.

astro-ph.GA↗

arXiv2021

Observational scalings testing modified gravity

We consider different observational effects to test modified gravity approach involving the cosmological constant in the common description of the dark matter and the dark energy. We obtain upper limits for the cosmological constant by studying the scaling relations for 12 nearby galaxy clusters, the radiated power from gravitational waves and the Tully-Fisher relation for super spiral galaxies. Our estimations reveal that, for all these cases the upper limits for $\Lambda$ are consistent with its actual value predicted by the cosmological observations.

astro-ph.CO↗

arXiv2021

Hubble tension and absolute constraints on the local Hubble parameter

It is shown, from the two independent approaches of McCrea-Milne and of Zeldovich, that one can fully recover the set equations corresponding to the relativistic equations of the expanding universe of Friedmann-Lemaitre-Robertson-Walker geometry. Although similar, the Newtonian and relativistic set of equations have a principal difference in the content and hence define two flows, local and global ones, thus naturally exposing the Hubble tension at the presence of the cosmological constant \Lambda. From this, we obtain absolute constraints on the lower and upper values for the local Hubble parameter, \sqrt{\Lambda c^2/3} \simeq 56.2$ and \sqrt{\Lambda c^2} \simeq 97.3 (km/sec Mpc^{-1}), respectively. The link to the so-called maximum force--tension issue in cosmological models is revealed.

astro-ph.CO↗

arXiv2021

Cosmic voids and induced hyperbolicity. III. tracing redshift dependence

The currently released datasets of the observational surveys reveal the redshift dependence of the physical features of cosmic voids. We study the void induced hyperbolicity, that is the deviation of the photon beams propagating the voids, taking into account the redshift dependence of the void size indicated by the observational surveys. The cumulative image distortion parameter is obtained for the case of a sequence of variable size voids and given underdensity parameters. The derived formulae applied along with those of redshift distortion ones, enable one to trace the number and the physical parameters of the line-of-sight voids from the analysis of the distortion in the galactic surveys.}

gr-qc↗

arXiv2021

Cosmological constant, information and gedanken experiments with black hole horizons

The cosmological constant if considered as a fundamental constant, provides an information treatment for gravitation problems, both cosmological and of black holes. The efficiency of that approach is shown via gedanken experiments for the information behavior of the horizons for Schwarzschild-de Sitter and Kerr-de Sitter metrics. A notion of entropy regarding any observer and in all possible non-extreme black hole solutions is suggested, linked also to Bekenstein bound. The suggested information approach forbids the existence of naked singularities.

gr-qc↗

arXiv2021

Cosmic voids and induced hyperbolicity. II. Sensitivity to void/wall scales

Cosmic voids as typical under-density regions in the large scale Universe are known for their hyperbolic properties as an ability to deviate the photon beams. The under-density then is acting as the negative curvature in the hyperbolic spaces. The hyperbolicity of voids has to lead to distortion in the statistical analysis at galactic surveys. We reveal the sensitivity of the hyperbolicity and hence of the distortion with respect to the ratio of void/wall scales which are observable parameters. This provides a principal possibility to use the distortion in the galactic surveys in revealing the line-of sight number of cosmic voids and their characteristic scales.

gr-qc↗

arXiv2021

Hubble tension vs two flows

The Hubble tension is shown to be solvable, without any free parameter, conceptually and quantitatively, within the approach of modified weak-field General Relativity involving the cosmological constant $\Lambda$. That approach enables one to describe in a unified picture both the dynamics of dark matter containing galaxies and the accelerated expansion of the Universe, thus defining a {\it local} Hubble constant of a local flow and the {\it global} one. The data on the dark matter content of peculiar galaxy samples are shown to be compatible to that unified picture. Future more refined surveys of galaxy distribution, hierarchical dynamics and flows within the vicinity of the Local group and the Virgo supercluster can be decisive in revealing the possible common nature of the dark sector.

gr-qc↗

arXiv2021

Black hole shadow to probe modified gravity

We study the black hole's shadow for Schwarzschild - de Sitter and Kerr - de Sitter metrics with the contribution of the cosmological constant \Lambda. Based on the reported parameters of the M87* black hole shadow we obtain constraints for the $\Lambda$ and show the agreement with the cosmological data. It is shown that, the coupling of the \Lambda-term with the spin parameter reveals peculiarities for the photon spheres and hence for the shadows. Within the parametrized post-Newtonian formalism the constraint for the corresponding \Lambda-determined parameter is obtained.

gr-qc↗

arXiv2020

Cosmic voids and induced hyperbolicity

Cosmic voids - the low density regions in the Universe - as characteristic features of the large scale matter distribution, are known for their hyperbolic properties. The latter implies the deviation of photon beams due to their underdensity, thus mimicing the negative curvature. We now show that the hyperbolicity can be induced not only by negative curvature or underdensity but also depends on the anisotropy of the photon beams.

gr-qc↗

arXiv2020

Lense-Thirring precession and gravito-gyromagnetic ratio

The geodesics of bound spherical orbits i.e. of orbits performing Lense-Thirring precession, are obtained in the case of the $\Lambda$-term within gravito-electromagnetic formalism. It is shown that the presence of the $\Lambda$-term in the equations of gravity leads to both relativistic and non-relativistic corrections in the equations of motion. The contribution of the $\Lambda$-term in the Lense-Thirring precession is interpreted as an additional relativistic correction and the gravito-gyromagnetic ratio is defined.

gr-qc↗

arXiv2020

The Djorgovski-Gurzadyan dark energy integral equation and the Hubble diagram

We consider the observational aspects of the value of dark energy density from quantum vacuum fluctuations based initially on the Gurzadyan-Xue model. We reduce the Djorgovski-Gurzadyan integral equation to a differential equation for the co-moving horizon and then, by means of the obtained explicit form for the luminosity distance, we construct the Hubble diagram for two classes of observational samples. For supernova and gamma-ray burst data we show that this approach provides viable predictions for distances up to $z \simeq 9$, quantitatively at least as good as those provided by the lambda cold dark matter ($\Lambda$CDM) model. The Hubble parameter dependence $H(z)$ of the two models also reveals mutual crossing at $z=0.4018$, the interpretation of which is less evident.

astro-ph.CO↗

arXiv2020

Lense-Thirring precession and modified gravity constraints

The orbital Lense-Thirring precession is considered in the context of constraints for weak-field General Relativity involving the cosmological constant $\Lambda$. It is shown that according to the current accuracy of satellite measurements the obtained error limits for $\Lambda$ is self-consistent with cosmological observations. The corrections of $\Lambda$ term are derived for the strong field Lense-Thirring precession i.e. the frame dragging effect and for the nutation. As a result, in the context of recently proposed $\Lambda$-gravity we obtain constraints for $\Lambda$ in both relativistic and weak-field limits. Namely, for the latter we analyze several Keplerian systems at different scales. We find that the obtained constraints for the modified gravity corrections are several orders of magnitude tighter than those available for such effects as gravitational redshift, gravitational time delay and geodetic precession in Solar System.

gr-qc↗

arXiv2020

Galactic sparsity and $\Lambda$-gravity

The sparsity parameter for clusters of galaxies is obtained in the context of $\Lambda$-gravity. It is shown that, the theoretical estimated values are within the reported error limits of the measured data. Thus, in the future the sparsity parameter can serve as an informative new test to detect the discrepancy between General Relativity and $\Lambda$-gravity.

gr-qc↗

arXiv2020

On the Lambda-evolution of galaxy clusters

The evolution of galaxy clusters can be affected by the repulsion described by the cosmological constant. This conclusion is reached within the modified weak-field General Relativity approach where the cosmological constant \Lambda enables to describe the common nature of the dark matter and the dark energy. Geometrical methods of theory of dynamical systems and the Ricci curvature criterion are used to reveal the difference in the instability properties of galaxy clusters which determine their evolutionary paths. Namely, it is shown that the clusters determined by the gravity with \Lambda-repulsion tend to become even more unstable than those powered only by Newtonian gravity, the effect to be felt at cosmological time scales.

astro-ph.CO↗

arXiv2019

On the role of dust in the microwave emission of galactic halos

The contribution of the thermal dust component in galactic halo rotation is explored based on the microwave data of Planck satellite. The temperature asymmetry of Doppler nature revealed for several edge-on galaxies at several microwave frequencies is analyzed regarding the contribution of the thermal dust emission. We derive the dust contribution to the galactic halo rotation using the data in three bands, 353GHz, 545GHz and 857GHz for two nearby galaxies M81 and M82. The relevance of the revealed properties on the halo rotation is then discussed in the context of the modified gravity theories proposed to describe the dark matter configurations.

astro-ph.GA↗

arXiv2019

H_0 tension: clue to common nature of dark sector?

The recently sharpened H_0 tension is argued not to be a result of data calibration or other systematic but an indication for the common nature of dark matter and dark energy. This conclusion is devised within modified weak-field General Relativity where the accelerated expansion of the Universe and the dynamics of galaxy groups and clusters are described by the same parameter, the cosmological constant. The common nature of the dark sector hence will result in intrinsic discrepancy/tension between the local and global determinations of values of the Hubble constant.

astro-ph.CO↗