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Items from 1 to 20 out of 494 results

article

Stability considerations of a Schwarzschild black hole with an $r$ dependent mass‐function

Peter Otto Hess, Enrique López‐Moreno

Astronomische Nachrichten > 342 > 7-8 > 1034 - 1043

The axial and polar modes for the ring down of a Schwarzschild black hole are calculated using an

r

‐dependent mass‐function and finally applying the asymptotic iteration method (AIM). We were able to reach up to 500 iterations, obtaining for the first time convergence for a wide range of large damping modes. The general relativity (GR) and an extended model with an

r

‐dependent mass‐function are compared...

article

Neutron star collisions and gravitational waves

Matthias Hanauske, Lukas R. Weih

Astronomische Nachrichten > 342 > 5 > 788 - 798

The long‐awaited detection of a gravitational wave from the merger of a binary neutron star in August 2017 (GW170817) marked the beginning of the new field of multi‐messenger gravitational wave astronomy. By exploiting the extracted tidal deformations of the two neutron stars from the late inspiral phase of GW170817, it was possible to constrain several global properties of the equation of state of...

article

Precession of triaxially deformed neutron stars

Yong Gao, Lijing Shao

Astronomische Nachrichten > 342 > 1-2 > 364 - 368

A deformed neutron star (NS) will precess if the instantaneous spin axis and the angular momentum are not aligned. Such a precession can produce continuous gravitational waves (GWs) and modulate electromagnetic pulse signals of pulsars. In this contribution, we extend our previous work in a more convenient parameterization. We treat NSs as rigid triaxial bodies and give analytical solutions for angular...

article

Discontinuity g‐modes of hybrid stars: Effect of sequential phase transitions

Maria Camila Rodríguez, Ignacio F. Ranea‐Sandoval, Mauro Mariani, Germán Malfatti, more

Astronomische Nachrichten > 342 > 1-2 > 305 - 309

The detection of event GW170817 and its electromagnetic counterpart started the era of multi‐messenger astronomy with gravitational waves. The observational constraints from this event and the estimation of mass and radius of PSR J0030 + 0451 is being used to get insights related to the nature of matter inside these compact objects. In this work, we construct hybrid equations of state using modern...

article

Axial ring‐down modes in general relativity and in its pseudo‐complex extension

Peter O. Hess, Enrique López‐Moreno

Astronomische Nachrichten > 342 > 1-2 > 135 - 141

We calculate the axial ring‐down frequencies of the merger of two black holes, using a modified version of the pseudo‐complex General Relativity (pc‐GR) and comparing it with the standard General Relativity (GR). The path, on how to determine the axial modes, serve as a starting point for more general extensions of GR, involving additions of r‐dependent functions to g₀₀.

article

A minimal length uncertainty approach to cosmological constant problem

Abdel Magied Diab, Abdel Nasser Tawfik

Astronomische Nachrichten > 342 > 1-2 > 49 - 53

Based on quantum mechanical framework for the minimal length uncertainty, we demonstrate that the generalized uncertainty principle (GUP) parameter could be best constrained by recent gravitational waves observations on one hand. On the other hand, this suggests modified dispersion relations (MDRs) enabling an estimation for the difference between the group velocity of gravitons and that of photons...

article

Formation, propagation and detection of gravitational waves

Mohamed Armoon Shaliq, R. Sharath Prasanna

Journal of Mechanical and Energy Engineering > 2020 > Vol. 4, No 2 > 189--196

Gravitational Waves are a new form of energy that is too sensitive to measure. The study of Gravitational Waves paves a unique way to approach the new era of universal science. It is quite interesting to note that experimental proof of the early theory of Einstein is successfully proven after many years. The manuscript depicts the concepts of Gravitational Waves, propagation of Gravitational Waves,...

article

Gravitational Waves and Helicity in Undoped Graphene

Francesco Sorge

Annalen der Physik > 532 > 7 > n/a - n/a

The behavior of a monolayer undoped graphene sheet in presence of a weak gravitational wave is discussed. In the low‐energy limit, the linear dispersion of the energy levels near the Dirac points can be ascribed to massless excitations obeying a Dirac equation in a 2+1D spacetime. Starting from a 2+1 dimensional (2+1D) Lagrangian, the equations of motion for the electron (hole) wavefunction in the...

article

In-orbit operations of AGILE mission: 11 years successfully in space

Fabio D’Amico, Marco Tavani, Giovanni Annoni, Cristiano Contini, more

Rendiconti Lincei. Scienze Fisiche e Naturali > 2019 > 30 > 1 > 231-240

Astrorivelatore Gamma ad Immagini LEggero (AGILE) is a high-energy scientific space program funded by the Agenzia Spaziale Italiana (ASI—Italian Space Agency); the mission was developed and is being operated in cooperation with INAF, INFN, CIFS and with the participation of several Italian companies. The satellite was launched from India on April 23rd, 2007 in an LEO equatorial orbit. The scientific...

article

Binary neutron stars gravitational wave detection based on wavelet packet analysis and convolutional neural networks

Bai-Jiong Lin, Xiang-Ru Li, Wo-Liang Yu

Frontiers of Physics > 2020 > 15 > 2 > 1-7

This work investigates the detection of binary neutron stars gravitational wave based on convolutional neural network (CNN). To promote the detection performance and efficiency, we proposed a scheme based on wavelet packet (WP) decomposition and CNN. The WP decomposition is a time-frequency method and can enhance the discriminant features between gravitational wave signal and noise before detection...

article

AGILE search for gamma-ray counterparts of gravitational wave events

Francesco Verrecchia, Marco Tavani, Andrea Bulgarelli, Martina Cardillo, more

Rendiconti Lincei. Scienze Fisiche e Naturali > 2019 > 30 > 1 > 71-77

AGILE is a space mission of the Italian Space Agency dedicated to X-ray and gamma-ray astrophysics operating since 2007. Since the discovery of gravitational wave (GW) events by the LIGO-Virgo Collaboration (LVC) announced in February 2016, AGILE is playing a very important role in the search for possible X-ray and gamma-ray counterparts. The large fields of view of the gamma-ray and hard X-ray imagers...

article

Topical collection: Testing the Kerr spacetime with gravitational-wave and electromagnetic observations

Emanuele Berti

General Relativity and Gravitation > 2019 > 51 > 11 > 1-3

One of the Holy Grails of observational astronomy is to confirm the prediction that black holes in the Universe are described by the Kerr solution of Einstein’s field equations of general relativity. This Topical Collection provides a status report of theoretical and experimental progress towards confirming the “Kerr paradigm” through X-ray astronomy, gravitational lensing, stellar tidal disruption...

article

Calculation of Phase Velocities in the Field of Sea Surface Waves

K. V. Pokazeev, A. S. Zapevalov

Moscow University Physics Bulletin > 2019 > 74 > 4 > 413-418

Specific features of phase velocities of sea waves due to the angular distribution of wave energy and the second harmonic of a dominant wave with a velocity differing from the phase velocity of a free wave at the same frequency have been analyzed. The presence of wave components with different velocity projections on a given direction or different propagation velocities leads to a deviation in the...

article

Dark Matter Objects: Possible New Source of Gravitational Waves

C. Sivaram, Kenath Arun

Earth, Moon, and Planets > 2019 > 123 > 1-2 > 9-13

Gravitational waves from mergers of black holes and neutron stars are now being detected by LIGO. Here we look at a new source of gravitational waves, i.e., a class of dark matter objects whose properties were earlier elaborated. We show that the frequency of gravitational waves and strains on the detectors from such objects (including their mergers) could be within the sensitivity range of LIGO....

article

Numerical Relativity and the Discovery of Gravitational Waves

Robert A. Eisenstein

Annalen der Physik > 531 > 8 > n/a - n/a

Solving Einstein's equations precisely for strong‐field gravitational systems is essential to determining the full physics content of gravitational wave detections. Without these solutions it is not possible to infer precise values for initial and final‐state system parameters. Obtaining these solutions requires extensive numerical simulations, as Einstein's equations governing these systems are much...

article

GRID: a student project to monitor the transient gamma-ray sky in the multi-messenger astronomy era

Jiaxing Wen, Xiangyun Long, Xutao Zheng, Yu An, more

Experimental Astronomy > 2019 > 48 > 1 > 77-95

The Gamma-Ray Integrated Detectors (GRID) is a space mission concept dedicated to monitoring the transient gamma-ray sky in the energy range from 10 keV to 2 MeV using scintillation detectors onboard CubeSats in low Earth orbits. The primary targets of GRID are the gamma-ray bursts (GRBs) in the local universe. The scientific goal of GRID is, in synergy with ground-based gravitational wave (GW) detectors...

article

Geometric Algebra, Gravity and Gravitational Waves

Anthony N. Lasenby

Advances in Applied Clifford Algebras > 2019 > 29 > 4 > 1-41

We discuss an approach to gravitational waves based on Geometric Algebra and Gauge Theory Gravity. After a brief introduction to Geometric Algebra (GA), we consider Gauge Theory Gravity, which uses symmetries expressed within the GA of flat spacetime to derive gravitational forces as the gauge forces corresponding to making these symmetries local. We then consider solutions for black holes and plane...

article

Gravitational wave solutions to linearized Jordan Brans Dicke theory on a cosmological background

Onder Dunya, Metin Arik

General Relativity and Gravitation > 2019 > 51 > 7 > 1-12

Approximate solutions of Jordan–Brans–Dicke (JBD) theory for perturbed scalar field and perturbed Robertson–Walker metric, were found for an era dominated by the scalar field. Solutions for the scale factor a(t) and the scalar field $$\phi (t)$$ ϕ(t) in unperturbed JBD theory are dependent on the $$\omega $$ ω parameter which determines how the scalar field is coupled to geometry of space–time....

article

The delay time of gravitational wave — gamma-ray burst associations

Bing Zhang

Frontiers of Physics > 2019 > 14 > 6 > 1-11

The first gravitational wave (GW) — gamma-ray burst (GRB) association, GW170817/GRB 170817A, had an offset in time, with the GRB trigger time delayed by ∼1.7 s with respect to the merger time of the GW signal. We generally discuss the astrophysical origin of the delay time, Δt, of GW-GRB associations within the context of compact binary coalescence (CBC) — short GRB (sGRB) associations and GW burst...

article

Testing the nature of dark compact objects: a status report

Vitor Cardoso, Paolo Pani

Living Reviews in Relativity > 2019 > 22 > 1 > 1-104

Very compact objects probe extreme gravitational fields and may be the key to understand outstanding puzzles in fundamental physics. These include the nature of dark matter, the fate of spacetime singularities, or the loss of unitarity in Hawking evaporation. The standard astrophysical description of collapsing objects tells us that massive, dark and compact objects are black holes. Any observation...

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Search results

Stability considerations of a Schwarzschild black hole with an $r$ dependent mass‐function

Neutron star collisions and gravitational waves

Precession of triaxially deformed neutron stars

Discontinuity g‐modes of hybrid stars: Effect of sequential phase transitions

Axial ring‐down modes in general relativity and in its pseudo‐complex extension

A minimal length uncertainty approach to cosmological constant problem

Formation, propagation and detection of gravitational waves

Gravitational Waves and Helicity in Undoped Graphene

In-orbit operations of AGILE mission: 11 years successfully in space

Binary neutron stars gravitational wave detection based on wavelet packet analysis and convolutional neural networks

AGILE search for gamma-ray counterparts of gravitational wave events

Topical collection: Testing the Kerr spacetime with gravitational-wave and electromagnetic observations

Calculation of Phase Velocities in the Field of Sea Surface Waves

Dark Matter Objects: Possible New Source of Gravitational Waves

Numerical Relativity and the Discovery of Gravitational Waves

GRID: a student project to monitor the transient gamma-ray sky in the multi-messenger astronomy era

Geometric Algebra, Gravity and Gravitational Waves

Gravitational wave solutions to linearized Jordan Brans Dicke theory on a cosmological background

The delay time of gravitational wave — gamma-ray burst associations

Testing the nature of dark compact objects: a status report

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