Shape parameters of Galactic open clusters

(abridged) In this paper we derive observed and modelled shape parameters (apparent ellipticity and orientation of the ellipse) of 650 Galactic open clusters identified in the ASCC-2.5 catalogue. We provide the observed shape parameters of Galactic open clusters, computed with the help of a multi-component analysis. For the vast majority of clusters these parameters are determined for the first time. High resolution ("star by star") N-body simulations are carried out with the specially developed $\phi$GRAPE code providing models of clusters of different initial masses, Galactocentric distances and rotation velocities. The comparison of models and observations of about 150 clusters reveals ellipticities of observed clusters which are too low (0.2 vs. 0.3), and offers the basis to find the main reason for this discrepancy. The models predict that after $\approx 50$ Myr clusters reach an oblate shape with an axes ratio of $1.65:1.35:1$, and with the major axis tilted by an angle of $q_{XY} \approx 30^\circ$ with respect to the Galactocentric radius due to differential rotation of the Galaxy. Unbiased estimates of cluster shape parameters require reliable membership determination in large cluster areas up to 2-3 tidal radii where the density of cluster stars is considerably lower than the background. Although dynamically bound stars outside the tidal radius contribute insignificantly to the cluster mass, their distribution is essential for a correct determination of cluster shape parameters. In contrast, a restricted mass range of cluster stars does not play such a dramatic role, though deep surveys allow to identify more cluster members and, therefore, to increase the accuracy of the observed shape parameters.Comment: 13 pages, 12 figures, accepted for publication in Astronomy and Astrophysic

Formation and Evolution of Black Holes in Galactic Nuclei and Star Clusters

We study the formation, growth, and co-evolution of single and multiple supermassive black holes (SMBHs) and compact objects like neutron stars, white dwarfs, and stellar mass black holes in galactic nuclei and star clusters, focusing on the role of stellar dynamics. In this paper we focus on one exemplary topic out of a wider range of work done, the study of orbital parameters of binary black holes in galactic nuclei (binding energy, eccentricity, relativistic coalescence) as a function of initial parameters. In some cases the classical evolution of black hole binaries in dense stellar systems drives them to surprisingly high eccentricities, which is very exciting for the emission of gravitational waves and relativistic orbit shrinkage. Such results are interesting to the emerging field of gravitational wave astronomy, in relation to a number of ground and space based instruments designed to measure gravitational waves from astrophysical sources (VIRGO, Geo600, LIGO, LISA). Our models self-consistently cover the entire range from Newtonian dynamics to the relativistic coalescence of SMBH binaries

LISA observations of massive black hole mergers: event rates and issues in waveform modelling

The observability of gravitational waves from supermassive and intermediate-mass black holes by the forecoming Laser Interferometer Space Antenna (LISA), and the physics we can learn from the observations, will depend on two basic factors: the event rates for massive black hole mergers occurring in the LISA best sensitivity window, and our theoretical knowledge of the gravitational waveforms. We first provide a concise review of the literature on LISA event rates for massive black hole mergers, as predicted by different formation scenarios. Then we discuss what (in our view) are the most urgent issues to address in terms of waveform modelling. For massive black hole binary inspiral these include spin precession, eccentricity, the effect of high-order Post-Newtonian terms in the amplitude and phase, and an accurate prediction of the transition from inspiral to plunge. For black hole ringdown, numerical relativity will ultimately be required to determine the relative quasinormal mode excitation, and to reduce the dimensionality of the template space in matched filtering.Comment: 14 pages, 2 figures. Added section with conclusions and outlook. Matches version to appear in the proceedings of 10th Annual Gravitational Wave Data Analysis Workshop (GWDAW 10), Brownsville, Texas, 14-17 Dec 200

Massive binary black holes in galactic nuclei and their path to coalescence

Massive binary black holes form at the centre of galaxies that experience a merger episode. They are expected to coalesce into a larger black hole, following the emission of gravitational waves. Coalescing massive binary black holes are among the loudest sources of gravitational waves in the Universe, and the detection of these events is at the frontier of contemporary astrophysics. Understanding the black hole binary formation path and dynamics in galaxy mergers is therefore mandatory. A key question poses: during a merger, will the black holes descend over time on closer orbits, form a Keplerian binary and coalesce shortly after? Here we review progress on the fate of black holes in both major and minor mergers of galaxies, either gas-free or gas-rich, in smooth and clumpy circum-nuclear discs after a galactic merger, and in circum-binary discs present on the smallest scales inside the relic nucleus.Comment: Accepted for publication in Space Science Reviews. To appear in hard cover in the Space Sciences Series of ISSI "The Physics of Accretion onto Black Holes" (Springer Publisher

Muscle dysmorphia: Could it be classified as an addiction to body image?

BACKGROUND: Muscle dysmorphia (MD) describes a condition characterised by a misconstrued body image in which individuals who interpret their body size as both small or weak even though they may look normal or highly muscular. MD has been conceptualized as a type of body dysmorphic disorder, an eating disorder, and obsessive–compulsive disorder symptomatology. METHOD AND AIM: Through a review of the most salient literature on MD, this paper proposes an alternative classification of MD – the ‘Addiction to Body Image’ (ABI) model – using Griffiths (2005) addiction components model as the framework in which to define MD as an addiction. RESULTS: It is argued the addictive activity in MD is the maintaining of body image via a number of different activities such as bodybuilding, exercise, eating certain foods, taking specific drugs (e.g., anabolic steroids), shopping for certain foods, food supplements, and the use or purchase of physical exercise accessories). In the ABI model, the perception of the positive effects on the self-body image is accounted for as a critical aspect of the MD condition (rather than addiction to exercise or certain types of eating disorder). CONCLUSIONS: Based on empirical evidence to date, it is proposed that MD could be re-classified as an addiction due to the individual continuing to engage in maintenance behaviours that may cause long-term harm

Supermassive Black Hole Binaries: The Search Continues

Gravitationally bound supermassive black hole binaries (SBHBs) are thought to be a natural product of galactic mergers and growth of the large scale structure in the universe. They however remain observationally elusive, thus raising a question about characteristic observational signatures associated with these systems. In this conference proceeding I discuss current theoretical understanding and latest advances and prospects in observational searches for SBHBs.Comment: 17 pages, 4 figures. To appear in the Proceedings of 2014 Sant Cugat Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed. C.Sopuerta (Berlin: Springer-Verlag

Morphological Mutations of Dwarf Galaxies

Dwarf galaxies (DGs) are extremely challenging objects in extragalactic astrophysics. They are expected to originate as the first units in Cold Dark-Matter cosmology. They are the galaxy type most sensitive to environmental influences and their division into multiple types with various properties have invoked the picture of their variant morphological transformations. Detailed observations reveal characteristics which allow to deduce the evolutionary paths and to witness how the environment has affected the evolution. Here we review peculiarities of general morphological DG types and refer to processes which can deplete gas-rich irregular DGs leading to dwarf ellipticals, while gas replenishment implies an evolutionary cycling. Finally, as the less understood DG types the Milky Way satellite dwarf spheroidal galaxies are discussed in the context of transformation.Comment: 17 pages, 7 figures, Proceedings of Symposium 3 of JENAM 2010 "Dwarf Galaxies: Key to Galaxy Formation and Evolution", Polychronis Papaderos, Simone Recchi, Gerhard Hensler (Eds.), Springer Publisher, Heidelberg, ISBN 978-3-642-22017-