Cosmic Repulsion Research Articles

Possible influence of a cosmic repulsion on large-scale jets: Geometric viewpoint

Cosmic repulsion represented by a small positive value of the cosmological constant changes significantly properties of central gravitational fields at large distances, leading to existence of a static (or turnaround) radius where gravitational attraction of a center is just balanced by cosmic repulsion. Analyzing behavior of radial timelike geodesics in the Schwarzschild–de Sitter spacetime near its static radius we show that the particles with specific energy close to unity have tendency to slow down and cluster just below the static radius, forming clumps which, subsequently, start to expand uniformly due to cosmic repulsion. For central masses of (106–1011)M⊙ and current value of the cosmological constant 1.1×10−52m−2, this phenomenon takes place at distances of tens to hundreds of kiloparsecs from the center, being comparable with distances in which huge radio-lobes from some active galaxies were observed.

Stationary observers in Kerr-de Sitter spacetimes

In this paper, we present a study of basic classes of stationary observers orbiting in stationary and axially symmetric Kerr-de Sitter spacetimes. Along with proper definitions of these classes, we focus on their possible matching on particular circular orbits. Especially, we determine a number of such orbits in a given spacetime characterized by its rotational and cosmological parameters that leads to a comprehensive classification of the Kerr-de Sitter spacetimes. Studied profiles of orbital velocities of the observers and of forces keeping them on their orbits directly reflect complex structure of the Kerr-de Sitter spacetimes that is caused by a unique interplay of attraction and rotation of a central object and an ambient cosmic repulsion.

Influence of Cosmic Repulsion and Magnetic Fields on Accretion Disks Rotating around Kerr Black Holes

We present a review of the influence of cosmic repulsion and external magnetic fields on accretion disks rotating around rotating black holes and on jets associated with these rotating configurations. We consider both geometrically thin and thick disks. We show that the vacuum energy represented by the relic cosmological constant strongly limits extension of the accretion disks that is for supermassive black holes comparable to extension of largest galaxies, and supports collimation of jets at large distances from the black hole. We further demonstrate that an external magnetic field crucially influences the fate of ionized Keplerian disks causing creation of winds and jets, enabling simultaneously acceleration of ultra-high energy particles with energy up to 10 21 eV around supermassive black holes with M ∼ 10 10 M ⊙ surrounded by sufficiently strong magnetic field with B ∼ 10 4 G. We also show that the external magnetic fields enable existence of “levitating” off-equatorial clouds or tori, along with the standard equatorial toroidal structures, if these carry a non-vanishing, appropriately distributed electric charge.

Slowly decaying resonances of massive scalar fields around Schwarzschild-de Sitter black holes

We study in special limiting cases quasinormal modes of massive scalar fields in the Schwarzschild-de Sitter black hole backgrounds. We determine the lower limit on the mass parameter of the scalar field that allows the waves with quasinormal frequencies to propagate to infinity, showing that it depends on the spacetime parameters only. Then we discuss in the large multipole number limit quasinormal modes, whose frequencies can be directly related to the unstable circular photon geodesics. In the large scalar mass approximation, we demonstrate the new interesting phenomenon of slowly decaying resonances, that are strongly related to the maximum of the effective potential of the massive scalar field, which is located at the static radius of the Schwarzschild-de Sitter spacetimes, where the cosmic repulsion is just balanced by the black hole attraction.

Rotating black hole solutions with quintessential energy

Quintessential dark energy with density $\rho$ and pressure p is governed by an equation of state of the form $p=\omega_{q}\rho$ with the quintessential parameter $\omega_q\in (-1;-1/3)$ . We derive the geometry of quintessential rotating black holes, generalizing thus the Kerr spacetimes. Then we study the quintessential rotating black hole spacetimes with the special value of $\omega_{q} = -2/3$ when the resulting formulae are simple and easily tractable. We show that such special spacetimes can exist for the dimensionless quintessential parameter $c < 1/6$ and determine the critical rotational parameter a0 separating the black hole and naked singularity spacetime in dependence on the quintessential parameter c . For the spacetimes with $\omega_{q} = -2/3$ we give all the black hole characteristics and demonstrate local thermodynamical stability. We present the integrated geodesic equations in separated form and study in details the circular geodetical orbits. We give radii and parameters of the photon circular orbits, marginally bound and marginally stable orbits. We stress that the outer boundary on the existence of circular geodesics, given by the so-called static radius where the gravitational attraction of the black hole is balanced by the cosmic repulsion, does not depend on the dimensionless spin of the rotating black hole, similarly to the case of the Kerr-de Sitter spacetimes with vacuum dark energy. We also give restrictions on the dimensionless parameters c and a of the spacetimes allowing for existence of stable circular geodesics. Finally, using numerical methods we generalize the discussion of the circular geodesics to the black holes with arbitrary quintessential parameter $\omega_{q}$ .

Shadow of the rotating black hole with quintessential energy in the presence of plasma

We study the shadow of the rotating black hole with quintessential energy (i) in vacuum, (ii) in the presence of plasma with radial power-law density. For the vacuum case, the quintessential field parameter of the rotating black hole significantly changes the shape of the shadow. With increasing quintessential field parameter, the radius of the shadow also increases. With the increase of the radius of the shadow of the rotating black hole, the quintessential field parameter causes decrease of the distortion of the shadow shape: in the presence of the quintessential field parameter, the shadow of the fast rotating black hole becomes too close to the circle. We assume the distant observer of the black hole shadow to be located near the so-called static radius where the gravitational attraction of the black hole is just balanced by the cosmic repulsion. The shape and size of the shadow of quintessential rotating black hole surrounded by plasma depends on (i) plasma parameters, (ii) black hole spin and (iii) quintessential field parameter. With the increase of the plasma refraction index, the apparent radius of the shadow increases. However, for the large values of the quintessential field parameter, the change of the black hole shadow shape due to the presence of plasma is not significant, i.e. the effect of the quintessential field parameter dominates over the plasma effect.

The emergence of cosmic repulsion

In cosmology based on general relativity, the universe is modeled as a fluid. The transition from the Einstein field equation to its large-scale (cosmological) version is thus analogous to the transition, for a system consisting of a large number of molecules, from the molecular/kinetic description to thermodynamics and hydrodynamics. The cosmic fluid is an effective continuum defined on the cosmological scales (only); for such a continuum, the appearance of new emergent properties should be expected. (Emergence of space–time and gravity is not discussed here.) When these new properties are calculated, the following predictions result: (a) the universe is spatially flat; (b) its expansion is accelerating; (c) dark energy makes up 75% of the total energy density of the universe; (d) the pressure of dark energy is equal and opposite to its density. All of these are in good agreement with the observational data. Also in favor of the present model are the absence of adjustable parameters, and consistency with the second law of thermodynamics. The distance–redshift relation predicted by the model is in good agreement with the Hubble diagram of Type Ia supernovae.

Influence of the cosmic repulsion on the MOND model of the Magellanic Cloud motion in the field of Milky Way

It has been recently shown that the cosmic repulsion can have a highly significant influence on the motion of Magellanic Clouds (MC) in the gravitational field of Milky Way, treated in the framework of the Cold Dark Matter (CDM) halo model. However, there is an alternative to the CDM halo explanation of the rotation curves in the periphery of spiral galaxies, based on MOdified Newtonian Dynamics (MOND). Therefore, we study the role of the cosmic repulsion in the framework of the MOND theory applied to determine the MC motion. Our results demonstrate that in the MOND framework the influence of the cosmic repulsion on the motion of both Small and Large MC is also highly significant, but it is of a different character than in the framework of the CDM halo model. Moreover, we demonstrate that the MC motion in the framework of the CDM halo and MOND models is subtantially different and can serve as a test of these fundamentally different approaches to the explanation of the phenomena related to galaxies and the motion of satellite galaxies.

Atom &amp; cosmos: Einstein passes acceleration test: Data support dark energy as cause of cosmic repulsion

Science NewsVolume 181, Issue 9 p. 17-17 In the News Atom & cosmos: Einstein passes acceleration test: Data support dark energy as cause of cosmic repulsion Elizabeth Quill, Elizabeth QuillSearch for more papers by this author Elizabeth Quill, Elizabeth QuillSearch for more papers by this author First published: 25 April 2012 https://doi.org/10.1002/scin.5591810919Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume181, Issue95 May 2012Pages 17-17 RelatedInformation

Acceleration of string loops in the Schwarzschild-de Sitter geometry

We study acceleration of current-carrying string loops governed by the presence of an outer tension barrier and an inner angular momentum barrier in the field of Schwarzschild-de Sitter black holes. We restrict attention to the axisymmetric motion of string loops with energy high enough, when the string loop can overcome the gravitational attraction and escape to infinity. We demonstrate that string loops can be scattered near the black hole horizon, and the energy of string oscillations can be efficiently converted to the energy of their linear motion. Such a transmutation effect can potentially represent acceleration of jets in active galactic nuclei and microquasars. We give the conditions limiting energy available for conversion onto the jetlike motion. Surprisingly, we are able to show that string loops starting from rest can be accelerated up to velocities v\simc even in the field of Schwarzschild black holes, if their angular momentum parameter is low enough. Such loops could serve as an explanation of highly relativistic jets observed in some quasars and active galactic nuclei. The cosmic repulsion becomes important behind the so-called static radius where it accelerates the linear motion of the string loops up to velocity v=c that is reached at the cosmic horizon of the Schwarzschild-de Sitter spacetimes independently of the angular momentum parameter of the strings.

Influence of the cosmological constant on the motion of Magellanic Clouds in the gravitational field of Milky Way

Using the pseudo-Newtonian (PN) potential reflecting properties of the Schwarz-schild-de Sitter spacetime, we estimate the influence of the repulsive cosmological constant Λ ∼ 1.3 × 10−56cm−2 implied by recent cosmological tests onto the motion of both Small and Large Magellanic Clouds (SMC and LMC) in the gravitational field of the Milky Way. Considering detailed modelling of the gravitational field of the Galaxy disc, bulge and cold dark matter halo, the trajectories of SMC and LMC constructed for the PN potential with the cosmological constant are confronted to those given for Λ = 0. In the realistic model of the extended cold dark matter halo its edge and related total mass are taken at typical values reflecting recent diversity in the total Galaxy mass estimates. In all cases, strong influence of the cosmological constant, on 10% level or higher, has been found for motion of both SMC and LMC. Inside the halo, the Newtonian part of the PN potential is exact enough, while outside the halo the PN potential can give relevant relativistic corrections. The role of the cosmological constant is most conspicuous when binding mass is estimated for the satellite galaxies. We have found a strong influence of cosmic repulsion on the total binding mass for both galaxies. For SMC there is the binding mass MSMCΛ = 0 = 7.07 × 1011M⨀ and MSMCΛ > 0 = 8.61 × 1011M⨀, while even much higher increase is found for LMC, where MLMCΛ = 0 = 1.50 × 1012M⨀ and MLMCΛ > 0 = 2.21 × 1012M⨀, putting serious doubts on the possibility that the LMC is bounded by the Milky Way. However, the estimates of binding masses are strongly influenced by initial velocity of SMC and LMC; we took the values inferred for the IAU MW rotation velocity ∼ 220 km/s. Our results indicate very important role of the cosmic repulsion in the motion of interacting galaxies, clearly demonstrated in the case of the satellite SMC and LMC galaxies moving in the field of Milky Way. In some cases, the effect of the cosmic repulsion can be even comparable to the effects of the dynamical friction and the Andromeda Galaxy.

Dark entropy

We examine the consequences of a universe with a non-constant cosmological term in Einstein's equations and find that the Bianchi identities reduce to the first law of thermodynamics when cosmological term is identified as being proportional to the entropy density of the universe. This means that gravitating dark energy can be viewed as entropy, but more, the holographic principle along with the known expansion of the universe indicates that the entropy of the universe is growing with time and this leads to a cosmic repulsion that also grows with time. Direct implications of this result are calculated and shown to be in good accord with recent observational data.

Current-carrying string loops in black-hole spacetimes with a repulsive cosmological constant

Current-carrying string loop dynamics in Schwarzschild-de Sitter spacetimes characterized by the cosmological parameter $\ensuremath{\lambda}=\frac{1}{3}\ensuremath{\Lambda}{M}^{2}$ is investigated. With attention concentrated to the axisymmetric motion of string loops it is shown that the resulting motion is governed by the presence of an outer tension barrier and an inner angular momentum barrier that are influenced by the black hole gravitational field given by the mass $M$ and the cosmic repulsion given by the cosmological constant $\ensuremath{\Lambda}$. The gravitational attraction could cause capturing of the string having low energy by the black hole or trapping in its vicinity; with high enough energy, the string can escape (scatter) to infinity. The role of the cosmic repulsion becomes important in vicinity of the so-called static radius where the gravitational attraction is balanced by the cosmic repulsion---it is demonstrated both in terms of the effective potential of the string motion and the basin boundary method reflecting its chaotic character, that a potential barrier exists along the static radius behind which no trapped oscillations may exist. The trapped states of the string loops, governed by the interplay of the gravitating mass $M$ and the cosmic repulsion, are allowed only in Schwarzschild-de Sitter spacetimes with the cosmological parameter $\ensuremath{\lambda}&lt;{\ensuremath{\lambda}}_{\mathrm{trap}}\ensuremath{\sim}0.00497$. The trapped oscillations can extend close to the radius of photon circular orbit, down to ${r}_{\mathrm{mt}}\ensuremath{\sim}3.3M$.

Dark energy and universal antigravitation

Universal antigravitation, a new physical phenomenon discovered astronomically at distances of 5 to 8 billion light years, manifests itself as cosmic repulsion that acts between distant galaxies and overcomes their gravitational attraction, resulting in the accelerating expansion of the Universe. The source of the antigravitation is not galaxies or any other bodies of nature but a previously unknown form of mass/energy that has been termed dark energy. Dark energy accounts for 70 to 80% of the total mass and energy of the Universe and, in macroscopic terms, is a kind of continuous medium that fills the entire space of the Universe and is characterized by positive density and negative pressure. With its physical nature and microscopic structure unknown, dark energy is among the most critical challenges fundamental science faces in the twenty-first century.

The expansion of the universe and the cosmological constant problem

The discovery that the expansion of the universe is accelerating in time is a major discovery which still awaits adequate explanation. It is generally agreed that this implies a cosmic repulsion as a result of the existence of a cosmological constant ∧>0. However, estimates of ∧, based on calculations of the zero-point fluctuations of quantum fields are too large by over a hundred orders of magnitude. This result is obtained by summing the zero-point energies up to a large cutoff energy Ω, based on the Planck scale. Since there is no compelling reason for this choice, we argue that since all known quantum electrodynamic (QED) effects involves interaction with matter, a preferred choice should be based on causality and other considerations, leading to a much lower value for ∧.

Equilibrium conditions of spinning test particles in Kerr–de Sitter spacetimes

Equilibrium conditions and spin dynamics of spinning test particles are discussed in the stationary and axially symmetric Kerr–de Sitter black-hole or naked-singularity spacetimes. The general equilibrium conditions are established, but due to their great complexity, the detailed discussion of the equilibrium conditions and spin dynamics is presented only in the simple and most relevant cases of equilibrium positions in the equatorial plane and on the symmetry axis of the spacetimes. It is shown that due to the combined effect of the rotation of the source and the cosmic repulsion the equilibrium is spin dependent in contrast to the spherically symmetric spacetimes. In the equatorial plane, it is possible at the so-called static radius, where the gravitational attraction is balanced by the cosmic repulsion, for the spinless particles as well as for spinning particles with arbitrarily large φ-oriented spin or at any radius outside the ergosphere with a specifically given spin orthogonal to the equatorial plane. On the symmetry axis, the equilibrium is possible at any radius in the stationary region and is given by an appropriately tuned spin directed along the axis. At the static radii on the axis the spin of particles in equilibrium must vanish.

Relativistic thick discs in the Kerr–de Sitter backgrounds

Perfect fluid tori with a uniform distribution of the specific angular momentum, ℓ(r, θ) = const, orbiting the Kerr–de Sitter black holes or naked singularities are studied. It is well known that the structure of equipotential surfaces of such marginally stable tori reflects the basic properties of any tori with a general distribution of the specific angular momentum. Closed equipotential surfaces corresponding to stationary thick discs are allowed only in the spacetimes admitting stable circular geodesics. The last closed surface crosses itself in the cusp(s) enabling the outflow of matter from the torus due to the violation of hydrostatic equilibrium. The inner cusp enables an accretion onto the central object. The influence of the repulsive cosmological constant, Λ > 0, on the equipotential surfaces lies in the existence of the outer cusp (with a stabilizing effect on the thick discs) and in the strong collimation of open equipotential surfaces along the rotational axis. Both the effects take place near a so-called static radius where the gravitational attraction is just balanced by the cosmic repulsion. The outer cusp enables excretion, i.e., the outflow of matter from the torus into the outer space. The plus-family discs (which are always co-rotating in the black-hole backgrounds but can be counter-rotating, even with negative energy of the fluid elements, in some naked-singularity backgrounds) are thicker and more extended than the minus-family ones (which are always counter-rotating in all backgrounds). For co-rotating discs in the naked-singularity spacetimes, the potential well between the centre of the disc and its edges at the cusps is usually much higher than in the black-hole spacetimes. If the parameters of naked-singularity spacetimes are very close to the parameters of extreme black-hole spacetimes, the family of possible disc-like configurations includes members with two isolated discs where the inner one is always a counter-rotating accretion disc.

ASTRONOMY: Cosmic Motion Revealed

ASTRONOMY: Cosmic Motion Revealed

Implications of cosmic repulsion for gravitational theory

We present a general, model independent analysis of a recently detected apparent cosmic repulsion, and discuss its potential implications for gravitational theories, both standard and non-standard. In particular, we show that a negatively spatially curved universe acts like a diverging refractive medium to thus naturally cause galaxies to accelerate away from each other. Additionally, we show that it is possible for a cosmic acceleration to only be temporary, with some accelerating universes actually being able to subsequently recontract.

Cosmic repulsion

Cosmic repulsion