Narrow Results

I review the properties of degenerate fermion balls and investigate the dark matter distribution at galactic centers using NFW, Moore and isothermal density profiles. I show that dark matter becomes degenerate for particles masses of a few keV at distances less than a few parsec from the center of our galaxy. To explain the galactic center black hole of mass of ~ 3.5 × 10⁶ M_⊙ and a supermassive black hole of ~ 3 × 10⁹ M_⊙ at a redshift of 6.41 in SDSS quasars, the mass of the fermion ball is assumed to be between 3 × 10³ M_⊙ and 3.5 × 10⁶ M_⊙. This constrains the mass of the dark matter particle between 0.6 keV and 82 keV. The lower limit on the dark matter mass is improved to about 6 keV if exact solutions of Poisson's equation are used in the isothermal power law case. The constrained dark matter particle could be interpreted as a sterile neutrino.

Chaotic dynamics essentially defines the global properties of gravitating systems, including, probably, the basics of morphology of galaxies. We use the Ricci curvature criterion to study the degree of relative chaos (exponential instability) in core-halo gravitating configurations. We show the existence of a critical core radius when the system is least chaotic, while systems with both smaller and larger core radius will typically possess stronger chaotic properties.

Since there should be some hydrogen left over in galaxies that was not used up in making stars, it was proposed that there may be molecular hydrogen clouds that form due to the Jeans instability but are unable to collapse. To observe this (very small) component of dark matter a test was proposed using the cosmic microwave background (CMB) radiation in the direction of the Andromeda galaxy by looking at slight Doppler shifts caused by its rotation. This was seen. Later on, the same effect was seen in the direction of other galaxies in our neighbourhood. Here, after a quick look at the general background of the matter-energy content of the Universe, this development will be reviewed.

High energy transients make up a diverse and exotic class of objects, from terrestrial lightning to γ-ray bursts at cosmological distances. In this review, we provide a detailed look at some of the more exciting transients observed over the last few years by Swift and other high energy missions.

In this centenary year for general relativity, this paper presents a brief review of some key developments that have rendered the theory pivotal to our understanding of cosmic X-ray sources, galactic nuclei and cosmology — a complete transformation from the time when the 50th anniversary of the theory was celebrated The paper ends with a few speculative comments on possible future developments.

We consider the simplest model of modulation of the 3D Gaussian field in k-space by a non-uniformly oscillating function f₁(k) that imitates the baryon acoustic oscillations (BAO), and a model function f₂(k) reproducing the smoothed power spectrum of a galaxy clustering. This model is applied to statistical simulations of radial (shell-like) distributions with calculations of 1D power spectra and auto-correlation functions. It is shown that the radial distributions simulated relatively to different centres in a region of study include quasi-periodical components with a characteristic (BAO) scale 2π/k ∼ 100 h⁻¹ M_pc which can appear with rather high probability depending on a sampling length L_R and an amplitude A_m of the modulation. The averaging of a number of 1D correlation functions built from different centres of radial distributions leads to the mean 1D correlation function, which is qualitatively consistent with the standard 3D correlation function. Both the functions are characterized by a single wide peak at the BAO scale. We apply 1D statistical procedures to the sample of spectroscopic redshifts of the brightest cluster galaxies (BCGs) and show that the results turn out to be consistent with those obtained in our model simulations.

We employed general relativity (GR) successfully to describe the galactic velocity profiles. In this work we present a mapping of the density contours of galaxies, achieving good concordance with observational data. In our Solar neighbourhood, we found a mass density and density fall-off fitting observational data satisfactorily. Galactic masses are consistently seen to be lower than those deduced from the approaches relying upon dark matter. Our results indicate that GR is the key to an explanation of the stars’ high velocities in galaxies. Mapping galactic density contours directly from the dynamics opens a new window for predicting galactic structure.

We search for low-dimensional chaotic signatures in the optical lightcurve of the Kepler field blazar W2R 1926+42. The frequently used correlation integral method is employed in our analysis. We find no apparent evidence for the presence of low-dimensional chaos in the lightcurve. If further confirmed, these results could be of importance for modeling the blazar emission mechanisms.

We use a high-resolution simulation of a galaxy-sized dark matter halo, published simulated data as well as four cluster-sized haloes¹ to study the inner halo structure in a Lambda cold dark matter cosmology. We find that the circular velocity curves are substantially better described by SWTS^2,3 profiles than by NFW⁴ or Moore⁵ profiles. Our findings confirm that no asymptotic slope is reached and that the corresponding extrapolated density profiles reach a finite maximum density. We analyse the impact of our findings on the detectability of the gamma-ray signal from the central regions of the Milky Way (MW) and from dark matter substructures in its halo, if the dark matter in the Universe is made of weakly self-interacting particles which self-annihilate. We discuss detection strategies for current gamma-ray detectors. We in addition review recent work by other authors and comment on possible boosts due to effects of structure on very small scales.

In over two years of operation Fermi-LAT has revolutionized our knowledge of the gamma-ray sky. Interstellar gamma rays are part of this new era and allow unprecedented tests for models of cosmic rays in the Galaxy. The extension to lower energies with INTEGRAL/SPI data is also evolving. The global multi-wavelength luminosity of the Milky Way has been derived, with implications for the Galactic energy balance and the radio-FIR correlation.

We examine the evolution of the spatial counts-in-cells distribution of galaxies and show that the form of the galaxy distribution function does not change significantly as galaxies merge and evolve. In particular, bound merging pairs follow a similar distribution to that of individual galaxies. From the adiabatic expansion of the universe we show how clustering, expansion and galaxy mergers affect the clustering parameter b. We also predict the evolution of b with respect to redshift.

We consider statistical models that have been proposed for luminosity distributions for the globular clusters in the Milky Way and M31. Although earlier research showed that the cluster luminosity functions in those two galaxies were well fit by Gaussian distributions, subsequent investigations suggested that their luminosities were better fit by t-, rather than Gaussian, distributions. By applying the Bayesian Information Criterion, we do not find overwhelming statistical evidence that the t-distribution is superior to the Gaussian distribution as a model of luminosity distribution for the Milky Way. In the case of M31, we find moderate evidence that the Gaussian distribution is superior to the t-distribution. In neither case do we find strong evidence to support the use of one distribution over the other as a statistical model for the luminosities of the globular clusters in the Milky Way and M31. Consequently, we recommend that the Gaussian be retained as the statistical model for luminosity distribution. Moreover, we urge caution in the use of the Kolmogorov-Smirnov statistic to justify the choice of statistical models for globular cluster luminosity functions.

An overview is provided for 200 years of galactic studies at the Tartu Observatory. Galactic studies have been one of the main topics of studies in Tartu over the whole period of the history of the Observatory, starting from F.G.W. Struve and J.H. Mädler, followed by Ernst Öpik and Grigori Kuzmin, and continuing with the present generation of astronomers. Our goal was to understand better the structure, origin and evolution of stars, galaxies and the Universe.

Numerical models of spherically symmetric relativistic stellar clusters with anisotropic distribution function are developed by generalizing isotropic solutions with an energy cutoff.

We show that exoplanets in the M31 galaxy may be detected with the pixel-lensing method by using telescopes making high cadence observations of an ongoing microlensing event. Although the mean mass for detectable exoplanets is about 2 M_J, even small mass exoplanets (M_P < 20 M_⊕) can cause significant deviations, which are observable with large telescopes. We reanalysed the POINT-AGAPE microlensing event PA-99-N2. First, we test the robustness of the binary lens conclusion for this light curve. Second, we show that for such long duration and bright microlensing events, the efficiency for finding planetary-like deviations is strongly enhanced.

We report on the results from XMM-Newton observations of Mrk 766. The source showed the rapid and large amplitude flux variation throughout the observations. Especially, the source entered the dimmest state during the early phase of 2005 observation. In order to investigate the spectral variation accompanied by the flux change, we compared flux in two different energy bands. Such a plot is called as “flux-flux plot”. Interestingly, we found two different branches on the plot, when the source enters in the dimmest state. This result may suggest the different emission mechanisms in each branch.

Our preceding paper “Implementing Maxwell’s aether.……” (Paper I) concluded:- (A) Maxwell’s aether, ignored in Relativity, is a massless, quasi-superfluid continuum of extremely high negative charge density; (B) Fundamental particles are not infinitesimal singularities within the aether but develop their mass by being ‘made out of it’ (hence the name Continuum Theory) as finite-sized vortical constructs of its motion. So reproduction (‘auto-creation’) of more of them requires only the addition of suitable dynamical energy, with Ampere’s law providing charge-coupling in shear to get rotations. (C) In the resulting gravitational process, generating the Newtonian force simultaneously also generates a radial electric field, the Gravity-Electric (G-E) field, whose action on astronomical plasmas could explain the flat tangential velocity profiles of spiral galaxies without resort to Cold Dark Matter (CDM) if outward disc flow is present. One of the objectives here is to provide that flow by axial infall and to examine its consequences. But first, if particles are ‘made out of aether’ the associated random aether-charge motion will generate radiation (the CMB) and impose four distance-cumulative, wavelength-independent transmission effects upon electromagnetic waves. One of these – a redshift – we see here as the cosmic redshift, plus intrinsic redshifts in stellar and galaxy ‘atmospheres’. Such a redshift appears to have been reliably observed with caesium clocks over long ground-level paths in 1968 but, lacking an appreciation of its mechanism, its wide significance was doubted. In fact, our extrapolation to intergalactic conditions dispenses with the BigBang. The other 3 transmission effects are:- spectral line broadening, scattering and attenuation, each of which has significant astronomical/cosmological expression. If the cosmic redshift is not a velocity, the reason for Dark Energy vanishes. In the resulting no-expansion cosmology the Universe was originally equipped with randomly moving aether, from whose motion and energy content the entire mass content of the Universe has grown over time by auto-creation, the local rate of which experiences positive feedback and acceleration as gravitational accumulations drive energy levels higher. Hence the clumpiness of galaxy distributions. The infall of cosmogonally young material from the auto-creation auras of clusters has 3 major implications. (1) It completely inverts the Big Bang perspective that lowmetallicity material, widespread in galaxy haloes, is very ancient. (2) Quasi-axial infall of such broadly neutral material (mostly H) onto a Spiral will spread out in the galactic plane, driven radially from the ionizing bulge by the G-E field, maintaining constant tangential velocity; all without CDM. This pattern means that the arms, although trailing, are actually being blown outward (unwrapping). See Paper I for detail. For such ongoing disruption of Spirals to prevail so widely means that originally each must have started life as an a.m.-conserving, tightly-wound spiral of mostly neutral, cosmogonically young material (mainly H), in which G-E field action was minimal until star formation and ionization had set in. (3) In cluster interiors, other cluster members may deflect the two infall streams as they converge onto a Spiral, introducing a dynamical rotational couple near the centre, with an axis roughly in the galactic plane, to produce a Barred Spiral. Cessation of infall then results in endwise collapse of that bar, yielding a fattened Elliptical. Those are indeed typically concentrated in the centres of clusters and show a dearth of active star formation, consistent with being deprived of young infall. We present images and diagrams in support and elaboration of (2) and (3). The CT model for quasars provides large intrinsic redshift by the CT analogue of Transverse Doppler Effect and offers light-element synthesis by the evolutionary precipitation of a runaway rotational shrinkage, with mass annihilation and emission of a GRB. Of special interest, relative to the arm’s-length nature of BigBang cosmology, is that continuous auto-creation (CAC) cosmology is in principle available near-by for direct study and the development of strong observational constraints. In the context of (1), the very low metallicity (Pop II) of globular (star) clusters abundantly present in the haloes of galaxies points to them being (infallen?) local concentrations of quite young auto-creation. In that case the ‘blue straggler’ stars more recently formed in their core regions may be our youngest examples of ongoing auto-creation. In summary, CT offers a much more directly observable Universe, with no Big Bang, CDM, or Dark Energy, and a CMB that records the true temperature of intergalactic space along the path taken by the radiation. Its closely cavity-radiation character arises from the random aether’s transmission-related opacity (Olbers’ Paradox) of the infinite CT Universe. Fundamentally, the aether’s random motion constitutes all-penetrating random electromagnetic excitation at the atomic scale that may offer the accommodation between classical physics and stochastic quantum electrodynamics so long obstructed by Relativity Theory.

We derive an analytical expression of a shadow size as a function of a charge in the Reissner – Nordström (RN) metric. Using the derived expression we consider shadows for negative tidal charges and charges corresponding to naked singularities , where and M are black hole charge and mass, respectively. An introduction of a negative tidal charge q can describes black hole solutions in theories with extra dimensions, so following the approach we consider an opportunity to extend RN metric to negative , while for the standard RN metric is always non-negative. We found that for q > 9/8 black hole shadows disappear. Significant tidal charges q = −6.4 are not consistent with observations of a minimal spot size at the Galactic Center observed in mm-band, moreover, these observations demonstrate that in comparison with the Schwarzschild black hole a Reissner – Nordström black hole with a significant charge q ≈ 1 provides a better fit of recent observational data for the black hole at the Galactic Center.

A rotating supermassive black hole (SBH) interacts with stars in a galactic nucleus via torques due to dragging of inertial frames. If the stars orbit preferentially about an axis that is misaligned with the SBH's spin, the SBH will experience a net torque and its spin vector will precess; individual stellar orbits also precess about the instantaneous SBH spin vector, although at different rates depending on their orbital elements. Solution of the coupled, post-Newtonian equations describing this interaction reveals two evolutionary modes: sustained precession of the SBH; and damped precession, leading to alignment of the SBH spin with the nuclear angular momentum. Beyond a certain radius, stars interact gravitationally with each other in a time shorter than the Lense-Thirring time. Long-term evolution in this case is well described as uniform precession of the SBH about the cluster's rotational axis, with a stochastic contribution due to star-star interactions.

Strongly Lensed systems, and in particular gravitational arcs, are useful tools for a variety of astrophysical applications. Finding arcs in wide-field surveys such as the Dark Energy Survey (DES) requires automated algorithms to select arc candidates due to the large amount of data. In this contribution we present a new arcfinding method that uses the Mediatrix filamentation method coupled to a neural network to select arc candidates. We carry out a systematic comparison between this method and three other arcfinders available in the literature — Lenzen et al. (2004), Horesh et al. (2005), and More et al. (2012) — on a sample of arc simulated with the PaintArcs method.