scholarly journals Relativistic Effects in Orbital Motion of the S-Stars at the Galactic Center

Universe ◽  
2020 ◽  
Vol 6 (10) ◽  
pp. 177
Author(s):  
Rustam Gainutdinov ◽  
Yurij Baryshev
Keyword(s):  
Galactic Center ◽  
Strong Field ◽  
Equations Of Motion ◽  
Compact Object ◽  
Relativistic Effects ◽  
Momentum Tensor ◽  
Positive Energy ◽  
Sgr A ◽  
Ppn Parameters ◽  
Very High

The Galactic Center star cluster, known as S-stars, is a perfect source of relativistic phenomena observations. The stars are located in the strong field of relativistic compact object Sgr A* and are moving with very high velocities at pericenters of their orbits. In this work we consider motion of several S-stars by using the Parameterized Post-Newtonian (PPN) formalism of General Relativity (GR) and Post-Newtonian (PN) equations of motion of the Feynman’s quantum-field gravity theory, where the positive energy density of the gravity field can be measured via the relativistic pericenter shift. The PPN parameters β and γ are constrained using the S-stars data. The positive value of the Tg00 component of the gravity energy–momentum tensor is confirmed for condition of S-stars motion.

scholarly journals Relativistic aspects of the JPL planetary ephemeris

2009 ◽  
Vol 5 (S261) ◽  
pp. 155-158 ◽  
Author(s):  
W. M. Folkner
Keyword(s):  
Solar System ◽  
Time Variation ◽  
Gravitational Constant ◽  
Equations Of Motion ◽  
Relativistic Effects ◽  
Radio Tracking ◽  
Data Set ◽  
Inverse Square Law ◽  
Radio Signals ◽  
Ppn Parameters

AbstractThe orbits of the planets as represented by the JPL planetary ephemerides are now primarily determined by radio tracking of spacecraft. Analysis of the data and propagation of the orbits relies on an internally consistent set of equations of motion and propagation of radio signals including relativistic effects at the centimeter level. The planetary ephemeris data set can be used to test some aspects of the underlying theory such as estimates of PPN parameters γ and β, time variation in the gravitational constant G, rotation of the solar system relative to distant objects (Mach's principle), and place stringent limits on the possible violation of the inverse-square law.

scholarly journals Observing a black hole event horizon: (sub)millimeter VLBI of Sgr A*

2009 ◽  
Vol 5 (S261) ◽  
pp. 271-276 ◽  
Author(s):  
Vincent L. Fish ◽  
Sheperd S. Doeleman
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Strong Evidence ◽  
Galactic Center ◽  
Strong Field ◽  
Variable Component ◽  
Massive Black Hole ◽  
Black Hole Candidate ◽  
Long Baseline ◽  
Sgr A

AbstractVery strong evidence suggests that Sagittarius A*, a compact radio source at the center of the Milky Way, marks the position of a super massive black hole. The proximity of Sgr A* in combination with its mass makes its apparent event horizon the largest of any black hole candidate in the universe and presents us with a unique opportunity to observe strong-field GR effects. Recent millimeter very long baseline interferometric observations of Sgr A* have demonstrated the existence of structures on scales comparable to the Schwarzschild radius. These observations already provide strong evidence in support of the existence of an event horizon. (Sub)Millimeter VLBI observations in the near future will combine the angular resolution necessary to identify the overall morphology of quiescent emission, such as an accretion disk or outflow, with a fine enough time resolution to detect possible periodicity in the variable component of emission. In the next few years, it may be possible to identify the spin of the black hole in Sgr A*, either by detecting the periodic signature of hot spots at the innermost stable circular orbit or parameter estimation in models of the quiescent emission. Longer term, a (sub)millimeter VLBI “Event Horizon Telescope” will be able to produce images of the Galactic center emission to the see the silhouette predicted by general relativistic lensing. These techniques are also applicable to the black hole in M87, where black hole spin may be key to understanding the jet-launching region.

scholarly journals BlackHoleCam: Fundamental physics of the galactic center

2017 ◽  
Vol 26 (02) ◽  
pp. 1730001 ◽  
Author(s):  
C. Goddi ◽  
H. Falcke ◽  
M. Kramer ◽  
L. Rezzolla ◽  
C. Brinkerink ◽  
...  
Keyword(s):  
Event Horizon ◽  
Near Infrared ◽  
Galactic Center ◽  
Strong Field ◽  
Current Knowledge ◽  
Current Status ◽  
Electromagnetic Spectrum ◽  
Fundamental Physics ◽  
Gravitational Fields ◽  
Sgr A

Einstein’s General theory of relativity (GR) successfully describes gravity. Although GR has been accurately tested in weak gravitational fields, it remains largely untested in the general strong field cases. One of the most fundamental predictions of GR is the existence of black holes (BHs). After the recent direct detection of gravitational waves by LIGO, there is now near conclusive evidence for the existence of stellar-mass BHs. In spite of this exciting discovery, there is not yet direct evidence of the existence of BHs using astronomical observations in the electromagnetic spectrum. Are BHs observable astrophysical objects? Does GR hold in its most extreme limit or are alternatives needed? The prime target to address these fundamental questions is in the center of our own Milky Way, which hosts the closest and best-constrained supermassive BH candidate in the universe, Sagittarius A* (Sgr A*). Three different types of experiments hold the promise to test GR in a strong-field regime using observations of Sgr A* with new-generation instruments. The first experiment consists of making a standard astronomical image of the synchrotron emission from the relativistic plasma accreting onto Sgr A*. This emission forms a “shadow” around the event horizon cast against the background, whose predicted size ([Formula: see text]as) can now be resolved by upcoming very long baseline radio interferometry experiments at mm-waves such as the event horizon telescope (EHT). The second experiment aims to monitor stars orbiting Sgr A* with the next-generation near-infrared (NIR) interferometer GRAVITY at the very large telescope (VLT). The third experiment aims to detect and study a radio pulsar in tight orbit about Sgr A* using radio telescopes (including the Atacama large millimeter array or ALMA). The BlackHoleCam project exploits the synergy between these three different techniques and contributes directly to them at different levels. These efforts will eventually enable us to measure fundamental BH parameters (mass, spin, and quadrupole moment) with sufficiently high precision to provide fundamental tests of GR (e.g. testing the no-hair theorem) and probe the spacetime around a BH in any metric theory of gravity. Here, we review our current knowledge of the physical properties of Sgr A* as well as the current status of such experimental efforts towards imaging the event horizon, measuring stellar orbits, and timing pulsars around Sgr A*. We conclude that the Galactic center provides a unique fundamental-physics laboratory for experimental tests of BH accretion and theories of gravity in their most extreme limits.

TeV observations of the Galactic center and starburst galaxies

2013 ◽  
Vol 9 (S303) ◽  
pp. 29-42
Author(s):  
Mathieu de Naurois
Keyword(s):  
Black Hole ◽  
Cosmic Rays ◽  
Galactic Center ◽  
High Energy ◽  
Starburst Galaxies ◽  
Energy Emission ◽  
Very High Energy ◽  
Sgr A ◽  
High Energy Emission ◽  
Very High

AbstractThe vicinity of the Galactic center harbors many potential accelerators of cosmic rays (CR) that could shine in very-high-energy (VHE) γ-rays, such as pulsar wind nebulae, supernova remnants, binary systems and the central black hole Sgr A*, and is characterized by high gas density, large magnetic fields and a high rate of starburst activity similar to that observed in the core of starburst galaxies. In addition to these astrophysical sources, annihilation of putative WIMPs concentrated in the gravitational well could lead to significant high-energy emission at the Galactic center. The Galactic center region has been observed by atmospheric Cherenkov telescopes, and in particular by the H. E. S. S. array in Namibia for the last ten years above 150 GeV. This large data set, comprising more than 200 hours of observations, led to the discovery of a point-like source spatially compatible with the supermassive black hole Sgr A*, and to an extended diffuse emission, correlated with molecular clouds and attributed to the interaction of cosmic rays with the interstellar medium. Over the same time period, two starburst galaxies, namely M 82 and NGC 253, were detected at TeV energies after very deep exposures. Results from these ten years of observations of the Galactic center region and starburst galaxies at TeV energies are presented, and implications for the various very-high-energy emission mechanisms are discussed.

Post-Newtonian approximation of a new theory of gravity

1981 ◽  
Vol 59 (11) ◽  
pp. 1592-1608 ◽  
Author(s):  
R. B. Mann ◽  
J. W. Moffat
Keyword(s):  
Equations Of Motion ◽  
Multipole Expansion ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Newtonian Theory ◽  
Perihelion Precession ◽  
Motion Energy ◽  
Newtonian Approximation ◽  
Theory Of Gravity ◽  
Ppn Parameters

The post-Newtonian approximation is developed for a new theory of gravity based on a Hermitian metric gμν. The approximation gives Newtonian theory in lowest order, but differs from general relativity in post-Newtonian order. The equations of motion, energy–momentum conservation, and perihelion precession are investigated. The equations of motion are derivable from the conservation laws of the energy–momentum tensor. A multipole expansion of the metric is formulated, and the PPN parameters α, β, and γ are found all to be unity. Several new parameters occur, most notably I, which is related to the number density of fermions of a system.

scholarly journals The Galactic center pulsar SGR J1745–29

2013 ◽  
Vol 9 (S303) ◽  
pp. 444-448
Author(s):  
Geoffrey C. Bower
Keyword(s):  
Interstellar Medium ◽  
Galactic Center ◽  
Relativistic Effects ◽  
Compact Objects ◽  
Radio Observations ◽  
Interstellar Scattering ◽  
General Relativistic ◽  
Sgr A

AbstractThe discovery of the Galactic center pulsar SGR J1745–29 has provided an important new window into plasma processes in the Galactic center (GC) interstellar medium, the population of compact objects in the GC, and the prospects for probing general relativistic effects through timing of a Sgr A* pulsar companion. We discuss here radio observations of the pulsar and how they are providing fresh insights. In particular, our results show that recent pulsar surveys had the sensitivity to detect many pulsars in the GC region without significant losses due to interstellar scattering. This raise the question of why only this pulsar close to Sgr A* has been detected.

scholarly journals The second post-Newtonian light propagation and its astrometric measurement in the solar system

2015 ◽  
Vol 24 (07) ◽  
pp. 1550056 ◽  
Author(s):  
Xue-Mei Deng
Keyword(s):  
Light Propagation ◽  
Equations Of Motion ◽  
Relativistic Effects ◽  
Differential Measurement ◽  
Gravitational Fields ◽  
Astrometric Observation ◽  
Space Astrometry ◽  
Definition Of ◽  
Ppn Parameters ◽  
Near Future

The relativistic theories of light propagation are generalized by introducing two new parameters ς and η in the second post-Newtonian (2PN) order, in addition to the parametrized post-Newtonian (PPN) parameters γ and β. This new 2PN parametrized (2PPN) formalism includes the nonstationary gravitational fields and the influences of all kinds of relativistic effects. The multipolar components of gravitating bodies are taken into account as well at the first post-Newtonian (1PN) order. The equations of motion and their solutions of this 2PPN light propagation problem are obtained. Started from the definition of a measurable quantity, a gauge-invariant angle between the directions of two incoming photons for a differential measurement in astrometric observation is discussed and its formula is derived. For a precision level of a few microarcsecond (μas) for space astrometry missions in the near future, we further consider a model of angular measurement, the Laser Astrometric Test of Relativity (LATOR)-like missions. In this case, all terms with aimed at the accuracy of ~1μas are estimated.

scholarly journals Weighing massive neutron star with screening gravity: a look on PSR J0740 + 6620 and GW190814 secondary component

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Rafael C. Nunes ◽  
Jaziel G. Coelho ◽  
José C. N. de Araujo
Keyword(s):  
Modified Gravity ◽  
Strong Field ◽  
Compact Object ◽  
Hydrostatic Equilibrium ◽  
Secondary Component ◽  
Maximum Mass ◽  
Strong Constraint ◽  
Gravitational Effects ◽  
Massive Neutron Star ◽  
Very High

AbstractNeutron stars (NSs) are excellent natural laboratories to constrain gravity on strong field regime and nuclear matter in extreme conditions. Motivated by the recent discovery of a compact object with $$2.59^{+0.08}_{-0.09} M_\odot $$ 2 . 59 - 0.09 + 0.08 M ⊙ in the binary merger GW190814, if this object was a NS, it serves as a strong constraint on the NS equation of state (EoS), ruling out several soft EoSs favored by GW170817 event. In this work, we revisit the question of the maximum mass of NSs considering a chameleon screening (thin-shell effect) on the NS mass-radius relation, where the microscopic physics inside the NS is given by realistic soft EoSs. We find that from appropriate and reasonable combination of modified gravity, rotation effects and realistic soft EoSs, that it is possible to achieve high masses and explain GW190814 secondary component, and in return also NSs like PSR J0740 + 6620 (the most NS massive confirmed to date). It is shown that gravity can play an important role in estimating maximum mass of NSs, and even with soft EoSs, it is possible to generate very high masses. Therefore, in this competition of hydrostatic equilibrium between gravity and pressure (from EoS choice), some soft EoSs, in principle, cannot be completely ruled out without first taking into account gravitational effects.

scholarly journals Detection of relativistic effects on the S2 orbit with GRAVITY

2016 ◽  
Vol 11 (S322) ◽  
pp. 25-30
Author(s):  
Marion Grould ◽  
Frédéric H. Vincent ◽  
Thibaut Paumard ◽  
Guy Perrin
Keyword(s):  
Second Generation ◽  
Galactic Center ◽  
Relativistic Effects ◽  
Compact Source ◽  
Sagittarius A ◽  
Sgr A

AbstractThe second generation instrument of the VLTI, GRAVITY, is expected to reach an astrometric accuracy of about 10 μas. It will thus possible to probe the spacetime close to the compact source Sagittarius A* (Sgr A*) at the Galactic Center by using accurate astrometric observations of the second closest star to the Galactic Center, S2. In particular, we show that combining GRAVITY and spectrograph instruments will allow us to detect several relativistic effects such as pericenter advance or the Lense-Thirring effect.

scholarly journals Numerical methods for General Relativistic particles

2018 ◽  
Vol 14 (S342) ◽  
pp. 19-23
Author(s):  
Fabio Bacchini ◽  
Bart Ripperda ◽  
Alexander Y. Chen ◽  
Lorenzo Sironi
Keyword(s):  
Numerical Methods ◽  
Gravitational Lensing ◽  
Complex Dynamics ◽  
Equations Of Motion ◽  
Numerical Algorithms ◽  
Relativistic Effects ◽  
Compact Objects ◽  
Light Rays ◽  
Massive Particles ◽  
External Forces

AbstractWe present recent developments on numerical algorithms for computing photon and particle trajectories in the surrounding of compact objects. Strong gravity around neutron stars or black holes causes relativistic effects on the motion of massive particles and distorts light rays due to gravitational lensing. Efficient numerical methods are required for solving the equations of motion and compute i) the black hole shadow obtained by tracing light rays from the object to a distant observer, and ii) obtain information on the dynamics of the plasma at the microscopic scale. Here, we present generalized algorithms capable of simulating ensembles of photons or massive particles in any spacetime, with the option of including external forces. The coupling of these tools with GRMHD simulations is the key point for obtaining insight on the complex dynamics of accretion disks and jets and for comparing simulations with upcoming observational results from the Event Horizon Telescope.

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