A5085046045- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- Geophysics and Gravity Measurements
- Gamma-ray bursts and supernovae
- Cosmology and Gravitation Theories
- Black Holes and Theoretical Physics
- High-pressure geophysics and materials
- Stellar, planetary, and galactic studies
- Geophysics and Sensor Technology
- Astrophysics and Cosmic Phenomena
- Astrophysics and Star Formation Studies
- Quantum Electrodynamics and Casimir Effect
- Quantum Mechanics and Non-Hermitian Physics
- Solar and Space Plasma Dynamics
- Relativity and Gravitational Theory
- Astronomy and Astrophysical Research
- Radio Astronomy Observations and Technology
- Nonlinear Waves and Solitons
- Quantum, superfluid, helium dynamics
- Atomic and Subatomic Physics Research
- Experimental and Theoretical Physics Studies
- Galaxies: Formation, Evolution, Phenomena
- Particle Accelerators and Free-Electron Lasers
- Algebraic structures and combinatorial models
- Particle Detector Development and Performance
University of Tübingen
2016-2025
Aristotle University of Thessaloniki
2007-2023
National and Kapodistrian University of Athens
2023
National Astronomical Observatory of Japan
2017
China Academy of Space Technology
2016
Georgia Institute of Technology
2016
University of Geneva
2016
Institute for Space Astrophysics and Planetology
2014
National Institute for Astrophysics
2012
Sofia University "St. Kliment Ohridski"
2010
Advanced gravitational wave interferometers, currently under realization, will soon permit the detection of waves from astronomical sources. To open era precision astronomy, a further substantial improvement in sensitivity is required. The future space-based Laser Interferometer Space Antenna and third-generation ground-based observatory Einstein Telescope (ET) promise to achieve required improvements frequency ranges. vastly improved third generation observatories could detailed...
One century after its formulation, Einstein's general relativity (GR) has made remarkable predictions and turned out to be compatible with all experimental tests. Most of these tests probe the theory in weak-field regime, there are theoretical reasons believe that GR should modified when gravitational fields strong spacetime curvature is large. The best astrophysical laboratories strong-field gravity black holes neutron stars, whether isolated or binary systems. We review motivations...
Advanced gravitational wave detectors, currently under construction, are expected to directly observe signals of astrophysical origin. The Einstein Telescope (ET), a third-generation detector, has been proposed in order fully open up the emerging field astronomy. In this paper we describe sensitivity models for ET and investigate potential limits imposed by fundamental noise sources. A special focus is set on evaluating frequency band below 10 Hz where complex mixture seismic, gravity...
We present new results for pulsating neutron stars. have calculated the eigenfrequencies of modes that one would expect to be most important gravitational-wave sources: fundamental fluid f-mode, first pressure p-mode and w-mode, twelve realistic equations state. From this numerical data we inferred a set ``empirical relations'' between mode-frequencies parameters star (the radius R mass M). Some these relation prove surprisingly robust, show how they can used extract details (radius, mass,...
Large gravitational wave interferometric detectors, like Virgo and LIGO, demonstrated the capability to reach their design sensitivity, but transform these machines into an effective observational instrument for astronomy a large improvement in sensitivity is required. Advanced detectors near future third-generation observatories more than one decade will open possibility perform astronomical observations from Earth. An overview of possible science reaches technological progress needed...
Abstract The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it offer unique opportunities to address many key astrophysical questions in completely novel way. synergy with ground-based and space-born instruments the electromagnetic domain, by enabling multi-messenger observations, add further discovery potential of LISA. next decade is crucial prepare community LISA’s first observations. This review outlines...
Circumambient and galactic-scale environments are intermittently present around black holes that reside in active galactic nuclei. As supermassive impart energy on their host galaxy, so the environment affects dynamics of solar-mass objects gravitational waves emitted from non-vacuum asymmetric binaries. Only recently an exact general-relativistic solution has been found describes a Schwarzschild hole immersed dark matter halo Hernquist type. We perform extensive analysis generic geodesics...
In this review we summarize the current understanding of gravitational-wave driven instability associated with so-called r-modes in rotating neutron stars. We discuss nature r-modes, detailed mechanics and its potential astrophysical significance. particular results regarding spin-evolution nascent stars, detectability r-mode gravitational waves mechanisms limiting spin-rate accreting stars binary systems.
We present new results for pulsating stars in general relativity. First we show that the so-called gravitational-wave modes of a neutron star can be excited when gravitational wave impinges on star. Numerical simulations suggest may astrophysically relevant, and discuss whether they will observable with future detectors. also how such observations could lead to estimates both radius mass star, thus put constraints nuclear equation state.
We demonstrate explicitly the existence of a new family outgoing-wave normal modes pulsating relativistic stars, first such known that has no analogue in Newtonian stars. These were discovered earlier by authors toy model, where they called strongly damped modes. Kojima then found examples these realistic spherical polytropic stellar models. Here we give number arguments this unequivocally, and calculate large eigenfrequencies. Physically, arise directly from coupling fluid oscillations star...
We study the problem of detecting, and inferring astrophysical information from, gravitational waves from a pulsating neutron star. show that fluid f p modes, as well gravitational-wave w may be detectable sources in our own Galaxy, investigate how accurately frequencies damping rates these modes can inferred noisy data stream. Based on conclusions this discussion we propose strategy for revealing supranuclear equation state using star fingerprints: observed an mode. also discuss source...
In the present paper we study oscillations of fast rotating neutron stars with realistic equations state (EoS) within Cowling approximation. We derive improved empirical relations for gravitational wave asteroseismology $f$-modes, and first time consider not only quadrupolar but also modes higher spherical order ($l=|m|=3$, 4). After performing a systematic comparison polytropic EoS, show that found in this case approximately hold EoS. addition, these will change significantly even if...
We present the field equations governing equilibrium of rapidly rotating neutron stars in scalar-tensor theories gravity, as well representative numerical solutions. The conditions for presence a nontrivial scalar and deviations from general relativistic solutions are studied. Two examples examined---one case that is equivalent to Brans-Dicke theory second perturbatively Einstein's relativity weak regime, but can differ significantly strong fields. Our results show star models with exist...
It was shown recently that normalized relations between the moment of inertia (I), quadrupole (Q), and tidal deformability (Love number) exist for slowly rotating neutron stars they are almost independent equation state (EOS). We extend computation I–Q relation to models up mass-shedding limit show universality is lost. With increasing rotation rate, departs significantly from its slow-rotation limit, deviating 40% 75% strange stars. The deviation also EOS dependent a broad set hadronic...
We study in detail the f-mode secular instability for rapidly rotating neutron stars, putting emphasis on supermassive models which do not have a stable nonrotating counterpart. Such stars are thought to be generic outcome of merger two standard mass stars. In addition we take into account effects strong magnetic field and r-mode instability, that can drain substantial amount angular momentum. find gravitational wave signal emitted by supramassive reach above Advance LIGO sensitivity at...
The Kerr geometry admits the Carter symmetry, which ensures that geodesic equations are integrable. It is shown gravitational waveforms associated with extreme-mass-ratio inspirals involving a non-integrable compact object display `glitch' phenomena, where frequencies of waves increase abruptly, when orbit crosses certain spacetime regions known as Birkhoff islands. presence or absence these features in data from upcoming space-borne detectors will therefore allow not only for tests general...
Analog models of black holes have unequivocally proven to be extremely beneficial in providing critical information regarding hole spectroscopy, superradiance, quantum phenomena and most importantly Hawking radiation evaporation; topics that either recently begun bloom through gravitational wave observations or not yet been investigated astrophysical setups. Black analog experiments made astonishing steps toward the aforementioned directions are paramount understanding nature field....
We study scalar, electromagnetic and gravitational perturbations of a Reissner--Nordstr\"om--anti-de Sitter (RN-AdS) spacetime, compute its quasinormal modes (QNM's). confirm extend results previously found for Schwarzschild--anti-de (S-AdS) black holes. For ``large'' holes, whose horizon is much larger than the AdS radius, different classes are almost exactly isospectral; this isospectrality broken when hole's radius comparable to radius. provide very accurate fitting formulas QNM's, which...
A newly discovered instability in rotating neutron stars, driven by gravitational radiation reaction acting on the stars' $r$-modes, is shown here to set an upper limit spin rate of young stars. We calculate timescales for growth linear perturbations due reaction, and dissipation shear bulk viscosity, working second order a slow-rotation expansion within Newtonian polytropic stellar model. The results are very temperature-sensitive: hot stars ($T>10^9$ K), lowest-order $r$-modes unstable,...
Complex frequencies of the normal modes Reissner-Nordstr\"om black hole are computed by two independent methods. The first is a high-order WKB approach devised Schutz and Will extended Iyer for Schwarzschild case. second direct numerical integration using method developed Chandrasekhar Detweiler, thereby extending earlier results Gunter. agree with ones an error less than 1% lowest-order modes. For somewhat higher orders, techniques fail but continues to give eigenfrequencies that should be...
Quantum superintegrable systems in two dimensions are obtained from their classical counterparts, the quantum integrals of motion being corresponding by a symmetrization procedure. For each system deformed oscillator algebra, characterized structure function specific for system, is constructed, generators algebra functions motion. The energy eigenvalues to state with finite-dimensional degeneracy can then be an economical way solving equations satisfied function, results agreement ones...
We present a case study for the relevance of r-mode instability accreting compact stars. Our estimates are based on approximations that facilitate "back envelope" calculations. discuss two different cases. (1) For recycled millisecond pulsars, we argue may be active at rotation periods longer than Kepler period (which provides dynamical limit rotation) as long core temperature is larger about 2 × 105 K. suggest have played role in evolution fastest spinning pulsars and it presently recently...