17,301 research outputs found
Orbital circularisation of white dwarfs and the formation of gravitational radiation sources in star clusters containing an intermediate mass black hole
(abbreviated) We consider how tight binaries consisting of a super-massive
black hole of mass and a white dwarf can be formed
in a globular cluster. We point out that a major fraction of white dwarfs
tidally captured by the black hole may be destroyed by tidal inflation during
ongoing circularisation, and the formation of tight binaries is inhibited.
However, some stars may survive being spun up to high rotation rates. Then the
energy loss through gravitational wave emission induced by tidally excited
pulsation modes and dissipation through non linear effects may compete with the
increase of pulsation energy due to dynamic tides. The semi-major axes of these
stars can be decreased below a 'critical' value where dynamic tides are not
effective because pulsation modes retain phase coherence between successive
pericentre passages. The rate of formation of such circularising stars is
estimated assuming that they can be modelled as polytropes and that
results of the tidal theory for slow rotators can be extrapolated to fast
rotators. We estimate the total capture rate as , where and
is the radius of influence of the black hole in units . We
find that the formation rate of tight pairs is approximately 10 times smaller
than the total capture rate. It is used to estimate the probability of
detection of gravitational waves coming from such tight binaries by LISA. We
conclude that LISA may detect such binaries provided that the fraction of
globular clusters with black holes in the mass range of interest is substantial
and that the dispersion velocity of the cluster stars near the radius of
influence of the black hole exceeds .Comment: accepted for publication in Astronomy and Astrophysics, minor
corrections in proof
On The Violation Of Marshall-Peierls Sign Rule In The Frustrated Heisenberg Antiferromagnet
We present a number of arguments in favor of the suggestion that the
Marshall-Peierls sign rule survives the frustration in the square-lattice
Heisenberg antiferromagnet with frustrating next-nearest-neighbor (diagonal)
bonds ( model) for relatively large values of the parameter
. Both the spin-wave analysis and the exact-diagonalization data
concerning the weight of Marshall states support the above suggestion.Comment: 8 pages, LaTex, 2 figurs on reques
Relativistic cross sections of mass stripping and tidal disruption of a star by a super-massive rotating black hole
[abbreviated] We consider the problem of tidal disruption of a star by a
super-massive Kerr black hole. Using a numerically fast Lagrangian model of the
tidally disrupted star we survey the parameter space of the problem and find
the regions in the parameter space where the total disruption of the star or a
partial mass loss take place as a result of fly-by around the black hole. Our
treatment is based on General Relativity, and we consider the range of the
black hole masses where the tidal disruption competes with the relativistic
effect of direct capture of the star by the black hole. We find that our
results can be represented on the plane of specific orbital angular momenta of
the star . We calculate the contours of a given mass
loss of the star on this plane, referred to as the tidal cross sections, for a
given black hole mass , rotational parameter and inclination of the
trajectory of the star with respect to the black hole equatorial plane. It is
shown that the tidal cross sections can be approximated as circles symmetric
above the axis , and shifted with respect to the origin of the
coordinates in direction of negative . The radii and shifts of
these circles are obtained numerically for the black hole masses in the range
and different values of . It is
shown that when the tidal disruption takes place for and when the tidal disruption is possible for .Comment: 11 pages, 16 figures, A&A in press, the text is clarified, the title
and the abstract shown in text are change
A model of gravitation with global U(1)-symmetry
It is shown that an embedding of the general relativity space into a flat
space gives a model of gravitation with the global symmetry and the
discrete one. The last one may be transformed into the symmetry
of the unified model, and the demand of independence of and
transformations leads to the estimate where
is an analog of the Weinberg angle of the standard model.Comment: 7 page
Semiclassical dynamics of domain walls in the one-dimensional Ising ferromagnet in a transverse field
We investigate analytically and numerically the dynamics of domain walls in a
spin chain with ferromagnetic Ising interaction and subject to an external
magnetic field perpendicular to the easy magnetization axis (transverse field
Ising model). The analytical results obtained within the continuum
approximation and numerical simulations performed for discrete classical model
are used to analyze the quantum properties of domain walls using the
semiclassical approximation. We show that the domain wall spectrum shows a band
structure consisting of 2 non-intersecting zones.Comment: 15 pages, 9 figure
- …