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Recent supernovae of type Ia measurements and other astronomical observations suggest that our universe is in accelerating phase of evolution at the present epoch. While a dark energy of unknown form is usually proposed as the most feasible…
We explain the effect of dark matter (flat rotation curve) using modified gravitational dynamics. We investigate in this context a low energy limit of generalized general relativity with a nonlinear Lagrangian ${\cal L}\propto R^n$, where…
We analyze several aspects of the recently noted neutron star collapse instability in close binary systems. We utilize (3+1) dimensional and spherical numerical general relativistic hydrodynamics to study the origin, evolution, and…
We study neutron star configurations in a simple shift-symmetric subfamily of degenerate higher-order scalar-tensor (DHOST) theories, whose deviations from General Relativity (GR) are characterized by a single parameter. We compute the…
The dynamical instability of new-born neutron stars is studied by evolving the linearized hydrodynamical equations. The neutron stars considered in this paper are those produced by the accretion induced collapse of rigidly rotating white…
The exploration of the low acceleration $a<a_{0}$ regime, where $a_{0}=1.2 \times 10^{-10}$m s$^{-2}$ is the acceleration scale of MOND around which gravitational anomalies at galactic scale appear, has recently been extended to the much…
Modified Gravity (MOG) and Non-Local Gravity (NLG) are two alternative theories to General Relativity. They are able to explain the rotation curves of spiral galaxies and clusters of galaxies without including dark matter (Moffat & Rahvar…
Gravitational waves are tiny disturbances in space-time and are a fundamental, although not yet directly confirmed, prediction of General Relativity. Rapidly rotating neutron stars are one of the possible sources of gravitational radiation…
Recent studies have thrown up a big enigma. On the one hand they point to satellite galaxies rotating faster than they should with the usual theory. On the other hand they also go against explanation of Newtonian gravity with dark matter.…
We apply the modified acceleration law obtained from Einstein gravity coupled explaining galaxy rotation curves without exotic dark matter. Our sample of galaxies includes low surface brightness (LSB) and high surface brightness (HSB)…
In the braneworld scenario the four dimensional effective Einstein equation has extra source terms, which arise from the embedding of the 3-brane in the bulk. These non-local effects, generated by the free gravitational field of the bulk,…
Orbital inclination is crucial in determining the mass of the binary. The astrometric excess noise contain the orbital motion information, which can be used to constrain the inclination. We aim to constrain the orbital inclination of a…
It is shown that for very rapidly rotating low mass strange stars the marginally stable orbit is located above the stellar surface. This effect is explained by the very important role of the oblateness of the rotating strange star. The…
Because most massive stars have been or will be affected by a companion during the course of their evolution, we cannot afford to neglect binaries when discussing the progenitors of supernovae and GRBs. Analyzing linear polarization in the…
We study relativistic stars in degenerate higher-order scalar-tensor theories that evade the constraint on the speed of gravitational waves imposed by GW170817. It is shown that the exterior metric is given by the usual Schwarzschild…
Neutron star (NS) binaries can be potentially intriguing gravitational wave (GW) sources, with both high- and low-frequency radiations from the possibly aspherical individual stars and the binary orbit, respectively. The successful…
The N-body dark matter (DM) simulations point that DM density profiles, e.g. the NFW halo, should be cuspy in its center, but observations disfavour this kind of DM profile. Here we consider whether the observed rotation curves "close" to…
The orbital period loss of the compact binary systems is the first indirect evidence of gravitational waves which agrees well with Einstein's general theory of relativity to a very good accuracy. However, there is less than one percent…
Precise astrometric measurement with Gaia satellite resulted in the discovery of tens of wide binary systems consisting of a Sun-like star and an invisible component. The latter can be a white dwarf, a neutron star, or a black hole. In this…
Gravitational-wave observations of compact binaries have the potential to uncover the distribution of masses and angular momenta of black holes and neutron stars in the universe. The binary components' physical parameters can be inferred…