Many Galactic black hole and neutron star sources in low X-ray mass binaries show QPOs (quasi periodic oscillations) in their observed X-ray fluxes, i.e. peaks in the Fourier variability power spectra. Pairs of twin peaks are observed, and in black-hole systems their frequencies (upp), (down) are in rational ratios. For example, in all four microquasars with twin peaks observed, (upp):(down) = 3:2. The rational ratios have been postulated in a model that explained twin peak QPOs as a non-linear resonance between modes of accretion disk oscillations. For those microquasars where the mass of the X-ray source is known, we determine the black-hole spin, following from the observed QPO frequencies within various models of resonance.
Read More
Many Galactic black hole and neutron star sources in low X-ray mass
binaries show QPOs (quasi periodic oscillations) in their observed X-ray
fluxes, i.e. peaks in the Fourier variability power spectra. Pairs of
twin peaks are observed, and in black-hole systems their frequencies
(upp), (down) are in rational ratios. For example, in all four
microquasars with twin peaks observed, (upp):(down) = 3:2. The rational
ratios have been postulated in a model that explained twin peak QPOs as
a non-linear resonance between modes of accretion disk oscillations. For
those microquasars where the mass of the X-ray source is known, we
determine the black-hole spin, following from the observed QPO
frequencies within various models of resonance.
Read More
The role of a nonzero cosmological constant is discussed for black-hole
or naked-singularity spacetimes, Einstein-Strauss vacuola spacetimes,
and general relativistic polytropic fluid spheres. In case of the
black-hole spacetimes, motion of test particles and photons and
equilibrium configurations of test perfect fluid are considered. Their
relevance to astrophysically very important accretion processes in disk
regime is established.
Read More
The role of a nonzero cosmological constant is discussed for black-hole or naked-singularity spacetimes, Einstein-Strauss vacuola spacetimes, and general relativistic polytropic fluid spheres. In case of the black-hole spacetimes, motion of test particles and photons and equilibrium configurations of test perfect fluid are considered. Their relevance to astrophysically very important accretion processes in disk regime is established.
Read More
Recent developments in the field of relativistic astrophysics related to accretion processes onto black holes and neutron stars, and to general phenomena connected to the properties of black holes, and the internal structure of neutron stars and quark stars, are discussed.
Read More
The influence of a repulsive cosmological constant on accretion processes onto black holes is discussed. The steady, spherically symmetric adiabatic inflow and outflow of perfect fluid is considered. Further, the attention is focused on the properties of both geometrically thin, Keplerian accretion disks and geometrically thick, toroidal disks having relevant pressure gradients. It is shown that nearby the static radius, where the gravitational attraction of a black hole is just balanced by the cosmological repulsion, the accretion toroidal disks have an outer cusp enabling outflow of matter from the disk. Behind the static radius the cosmological repulsion efficiently collimates jets that emanate along the rotation axis of the toroidal disk.
Read More
Recent developments in the field of relativistic astrophysics related to
accretion processes onto black holes and neutron stars, and to general
phenomena connected to the properties of black holes, and the internal
structure of neutron stars and quark stars, are discussed.
Read More
The influence of a repulsive cosmological constant on accretion
processes onto black holes is discussed. The steady, spherically
symmetric adiabatic inflow and outflow of perfect fluid is considered.
Further, the attention is focused on the properties of both
geometrically thin, Keplerian accretion disks and geometrically thick,
toroidal disks having relevant pressure gradients. It is shown that
nearby the static radius, where the gravitational attraction of a black
hole is just balanced by the cosmological repulsion, the accretion
toroidal disks have an outer cusp enabling outflow of matter from the
disk. Behind the static radius the cosmological repulsion efficiently
collimates jets that emanate along the rotation axis of the toroidal
disk.
Read More
The equilibrium of a charged test particle with spin located in the Reissner-Nordström background with a nonzero cosmological constant is investigated. The stationary equilibrium conditions resulting from the equations of motion and the equations of spin dynamics have to be satisfied simultaneously. It is shown that equilibrium conditions are independent of the spin of the test particle. For uncharged particles, they are satisfied at the so-called static radius, where gravitational attraction is exactly compensated for by cosmological repulsion. For charged particles, there is a variety of possible equilibria due to the electromagnetic interaction of the particle and the background. Any charged particle can be in an unstable equilibrium state between the black-hole and cosmological horizons of asymptotically de Sitter spacetimes, while sufficiently repulsed particles can be in an inner unstable equilibrium state and an outer stable equilibrium state above the horizon of asymptotically anti-de Sitter spacetimes. The separation-independent equilibrium is possible in extreme Reissner-Nordström spacetimes only.
Read More
The equilibrium of a charged test particle with spin located in the
Reissner-Nordström background with a nonzero cosmological constant
is investigated. The stationary equilibrium conditions resulting from
the equations of motion and the equations of spin dynamics have to be
satisfied simultaneously. It is shown that equilibrium conditions are
independent of the spin of the test particle. For uncharged particles,
they are satisfied at the so-called static radius, where gravitational
attraction is exactly compensated for by cosmological repulsion. For
charged particles, there is a variety of possible equilibria due to the
electromagnetic interaction of the particle and the background. Any
charged particle can be in an unstable equilibrium state between the
black-hole and cosmological horizons of asymptotically de Sitter
spacetimes, while sufficiently repulsed particles can be in an inner
unstable equilibrium state and an outer stable equilibrium state above
the horizon of asymptotically anti-de Sitter spacetimes. The
separation-independent equilibrium is possible in extreme
Reissner-Nordström spacetimes only.
Read More
