scholarly journals Bound on Photon Circular Orbits in General Relativity and Beyond

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 96
Author(s):  
Sumanta Chakraborty
Keyword(s):  
General Relativity ◽  
Circular Orbit ◽  
Strong Field ◽  
Normal Modes ◽  
Field Tests ◽  
Matter Content ◽  
Compact Objects ◽  
Circular Orbits ◽  
Higher Dimensional ◽  
Tests Of Gravity

The existence of a photon circular orbit can tell us a lot about the nature of the underlying spacetime, since it plays a pivotal role in the understanding of the characteristic signatures of compact objects, namely the quasi-normal modes and shadow radius. For this purpose, determination of the location of the photon circular orbit is of utmost importance. In this work, we derive bounds on the location of the photon circular orbit around compact objects within the purview of general relativity and beyond. As we have explicitly demonstrated, contrary to the earlier results in the context of general relativity, the bound on the location of the photon circular orbit is not necessarily an upper bound. Depending on the matter content, it is possible to arrive at a lower bound as well. This has interesting implications for the quasi-normal modes and shadow radius, the two key observables related to the strong field tests of gravity. Besides discussing the bound for higher dimensional general relativity, we have also considered how the bound on the photon circular orbits gets modified in the braneworld scenario, for pure Lovelock and general Lovelock theories of gravity. Implications of these results for compact objects were also discussed.

scholarly journals Post-Newtonian gravitational and scalar waves in scalar-Gauss-Bonnet gravity

2021 ◽  
Author(s):  
Banafsheh Shiralilou ◽  
Tanja Hinderer ◽  
Samaya Nissanke ◽  
Nestor Ortiz ◽  
Helvi Witek
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Gravitational Wave ◽  
Strong Field ◽  
Field Tests ◽  
Theoretical Modelling ◽  
Bonnet Gravity ◽  
Weak Coupling Approximation ◽  
Tests Of Gravity ◽  
The Impact

Abstract Gravitational waves emitted by black hole binary inspiral and mergers enable unprecedented strong-field tests of gravity, requiring accurate theoretical modelling of the expected signals in extensions of General Relativity. In this paper we model the gravitational wave emission of inspiralling binaries in scalar Gauss-Bonnet gravity theories. Going beyond the weak-coupling approximation, we derive the gravitational waveform to relative first post-Newtonian order beyond the quadrupole approximation and calculate new contributions from nonlinear curvature terms. We also compute the scalar waveform to relative 0.5PN order beyond the leading -0.5PN order terms. We quantify the effect of these terms and provide ready-to-implement gravitational wave and scalar waveforms as well as the Fourier domain phase for quasi-circular binaries. We also perform a parameter space study, which indicates that the values of black hole scalar charges play a crucial role in the detectability of deviation from General Relativity. We also compare the scalar waveforms to numerical relativity simulations to assess the impact of the relativistic corrections to the scalar radiation. Our results provide important foundations for future precision tests of gravity.

scholarly journals Galactic center pulsar as a test of black hole existence and properties

1979 ◽  
Vol 84 ◽  
pp. 401-404
Author(s):  
B. Paczyński ◽  
V. Trimble
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Galactic Center ◽  
Strong Field ◽  
Field Tests ◽  
Central Black Hole ◽  
X Ray ◽  
Tests Of General Relativity ◽  
Period Orbit ◽  
Short Period

There is a reasonable chance of finding a (probably X-ray) pulsar in a short-period orbit around the galactic center. Such a pulsar can provide a test distinguishing a central black hole from a supermassive object or spinar. It also makes available a good clock in a region of space in which GM/Rc2 is much larger than solar system values, thus allowing strong-field tests of general relativity.

scholarly journals The Square Kilometre Array

2007 ◽  
Vol 3 (S248) ◽  
pp. 164-169 ◽  
Author(s):  
A. R. Taylor
Keyword(s):  
Large Scale ◽  
Angular Resolution ◽  
Strong Field ◽  
Field Tests ◽  
Field Of View ◽  
Origin And Evolution ◽  
Reference Design ◽  
Formation And Evolution ◽  
Tests Of Gravity ◽  
Global Project

AbstractThe SKA is a global project to plan and construct the next-generation international radio telescope operating at metre to cm wavelengths. More than 50 institutes in 19 countries are involved in its development. The SKA will be an interferometric array with a collecting area of up to one million square metres and maximum baseline of at least 3000 km. The SKA reference design includes field-of-view expansion technology that will allow instantaneous imaging of up to several tens of degrees. The SKA is being designed to address fundamental questions in cosmology, physics and astronomy. The key science goals range from the epoch or re-ionization, dark energy, the formation and evolution of galaxies and large-scale structure, the origin and evolution of cosmic magnetism, strong-field tests of gravity and gravity wave detection, the cradle of life, and the search for extraterrestrial intelligence. The sensitivity, field-of-view and angular resolution of the SKA will make possible a program to create a multi-epoch data base of wide-angle relative astrometry to a few μas precision for ~10,000,000 radio sources with S > 10 μJy.

Strong-field tests of gravity with the double pulsar

2006 ◽  
Vol 15 (1-2) ◽  
pp. 34-42 ◽  
Author(s):  
M. Kramer ◽  
I.H. Stairs ◽  
R.N. Manchester ◽  
M.A. McLaughlin ◽  
A.G. Lyne ◽  
...  
Keyword(s):  
Strong Field ◽  
Field Tests ◽  
Tests Of Gravity

scholarly journals LOFT: the Large Observatory For X-ray Timing

2012 ◽  
Vol 8 (S290) ◽  
pp. 163-170
Author(s):  
Tomaso M. Belloni ◽  
Enrico Bozzo ◽  
Keyword(s):  
General Relativity ◽  
Strong Field ◽  
Compact Objects ◽  
High Time Resolution ◽  
General Description ◽  
X Ray ◽  
Equation Of States ◽  
Wide Range ◽  
First Time ◽  
New Discovery

AbstractLOFT, the large observatory for X-ray timing, is a new mission concept competing with other four candidates for a launch opportunity in 2022-2024. LOFT will be performing high-time resolution X-ray observations of compact objects, combining for the first time an unprecedented large collecting area for X-ray photons and a spectral resolution approaching that of CCD-based X-ray instruments (down to 200 eV FWHM at 6 keV). The operating energy range is 2-80 keV. The main science goals of LOFT are the measurement of the neutron stars equation of states and the test of General Relativity in the strong field regime. The breakthrough capabilities of the instruments on-board LOFT will permit to open also new discovery windows for a wide range of Galactic and extragalactic X-ray sources.In this contribution, we provide a general description of the mission concept and summarize its main scientific capabilities.

scholarly journals Strong gravity signatures in the polarization of gravitational waves

2019 ◽  
Vol 28 (14) ◽  
pp. 1944020 ◽  
Author(s):  
S. Shankaranarayanan
Keyword(s):  
General Relativity ◽  
Gravitational Wave ◽  
Gravitational Waves ◽  
Modified Gravity ◽  
Strong Field ◽  
Normal Modes ◽  
Strong Gravity ◽  
Modified Gravity Theories ◽  
Gravitational Wave Detectors ◽  
Gravity Theories

General Relativity is a hugely successful description of gravitation. However, both theory and observations suggest that General Relativity might have significant classical and quantum corrections in the Strong Gravity regime. Testing the strong field limit of gravity is one of the main objectives of the future gravitational wave detectors. One way to detect strong gravity is through the polarization of gravitational waves. For quasi-normal modes of black-holes in General Relativity, the two polarization states of gravitational waves have the same amplitude and frequency spectrum. Using the principle of energy conservation, we show that the polarizations differ for modified gravity theories. We obtain a diagnostic parameter for polarization mismatch that provides a unique way to distinguish General Relativity and modified gravity theories in gravitational wave detectors.

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