Related papers: Testing Strong-field Gravity with Quasi-Periodic O…
We perform the first study of the oscillation frequencies of rapidly rotating neutron stars in alternative theories of gravity, focusing mainly on the fundamental $f$-modes. We concentrated on a particular class of alternative theories -…
We study oscillations and instabilities of relativistic stars using perturbation theory in general relativity and take into account the contribution of a dynamic spacetime. We present the oscillation spectrum as well as the critical values…
This work explores the dynamic properties of test particles surrounding a distorted, deformed compact object. The astrophysical motivation was to choose such background, which could constitute a more reasonable model of a real situation…
X-rays trace accretion onto compact objects in binaries with low mass companions at rates ranging up to near Eddington. Accretion at high rates onto neutron stars goes through cycles with time-scales of days to months. At lower average…
In early 1996 a series of discoveries begun with NASA's Rossi X-ray Timing Explorer of a new, up to then unknown astrophysical phenomenon. It turned out that accreting low magnetic-field neutron stars show quasi-periodic oscillations in…
Using a metric perturbation method, we study gravitational waves from a test particle scattered by a spherically symmetric relativistic star. We calculate the energy spectrum and the waveform of gravitational waves for axial modes. Since…
Neutrinos do oscillate, which up to our best knowledge implies that they are massive particles. As such, neutrinos should interact with gravitational fields. As their masses are tiny, the gravitational fields must be extremely strong. In…
We derive the perturbation equations for relativistic stars in scalar-tensor theories of gravity and study the corresponding oscillation spectrum. We show that the frequency of the emitted gravitational waves is shifted proportionally to…
Future very-large-area X-ray instruments (for which the effective area is larger than $>3$m$^2$) will be able to measure the frequencies of quasi-periodic oscillations~(QPOs) observed in the X-ray flux from accreting compact objects with…
Quasi-normal oscillation modes of neutron stars provide a means to probe their interior composition using gravitational wave astronomy. We compute the frequencies and damping times of composition-dependent core g-modes of neutron stars…
Neutron stars (NSs) in scalar-tensor (ST) theories of gravitation can acquire scalar charges and generate distinct spacetimes from those in General Relativity (GR) through the celebrated phenomenon of spontaneous scalarization. Taking on an…
The first millisecond X-ray variability phenomena from accreting compact objects have recently been discovered with the Rossi X-ray Timing Explorer. Three new phenomena are observed from low-mass X-ray binaries containing low-magnetic-field…
We study torsional oscillations of neutron stars in the scalar-tensor theory of gravity using the relativistic Cowling approximation. We compute unperturbed neutron star models adopting realistic equations of state for the neutron star's…
The kilo-Hertz Quasi--Periodic Oscillations in X-ray binaries could originate within the accretion flow, and be a signature of non--linear fluid oscillations and mode coupling in strong gravity. The possibility to decipher these systems…
Recently discovered quasi periodic oscillations in the X-ray brightness of low mass X-ray binaries are used to derive constraints on the mass of the neutron star component and the equation of state of neutron star matter. The observations…
Correlations discovered between millisecond timing properties and spectral properties in neutron star x-ray binaries are described and then interpreted in relation to accretion flows in the systems. Use of joint timing and spectral…
In contrast to gravity in the weak-field regime, which has been subject to numerous experimental tests, gravity in the strong-field regime is largely unconstrained by observations. We show that gravity theories that cannot be rejected by…
We study the interaction of massless scalar fields with self-gravitating neutron stars by means of fully dynamic numerical simulations of the Einstein-Klein-Gordon perfect fluid system. Our investigation is restricted to spherical symmetry…
The effect of a slowly rotating mass on a forced harmonic oscillator with two degrees of freedom is studied in the weak field approximation. It is found that according to the general theory of relativity there is a shift in the resonat…
The detection of fast quasi-periodic variability from accreting black holes and neutron stars has been used to constrain their masses, radii, and spins. If the observed oscillations are linear modes in the accretion disks, then bounds can…