2,875 research outputs found
Observational Features of Black Holes
Recently considered a very attracting possibility to detect retro-MACHOs,
i.e. retro-images of the Sun by a Schwarzschild black hole. In this paper we
discuss glories (mirages) formed near rapidly rotating Kerr black hole horizons
and propose a procedure to measure masses and rotation parameters analyzing
these forms of mirages. In some sense that is a manifestation of gravitational
lens effect in the strong gravitational field near black hole horizon and a
generalization of the retro-gravitational lens phenomenon. We analyze the case
of a Kerr black hole rotating at arbitrary speed for some selected positions of
a distant observer with respect to the equatorial plane of a Kerr black hole.
We discuss glories (mirages) formed near rapidly rotating Kerr black hole
horizons and propose a procedure to measure masses and rotation parameters
analyzing these forms of mirages. Some time ago suggested to search shadows at
the Galactic Center. In this paper we present the boundaries for shadows
calculated numerically. We also propose to use future radio interferometer
RADIOASTRON facilities to measure shapes of mirages (glories) and to evaluate
the black hole spin as a function of the position angle of a distant observer.Comment: Plenary talk presented at Workshop on High Energy Physics&Field
Theory (Protvino, Russia, 2004
On integration of some classes of dimensional nonlinear Partial Differential Equations
The paper represents the method for construction of the families of
particular solutions to some new classes of dimensional nonlinear
Partial Differential Equations (PDE). Method is based on the specific link
between algebraic matrix equations and PDE. Admittable solutions depend on
arbitrary functions of variables.Comment: 6 page
Constraining the range of Yukawa gravity interaction from S2 star orbits
We consider possible signatures for Yukawa gravity within the Galactic
Central Parsec, based on our analysis of the S2 star orbital precession around
the massive compact dark object at the Galactic Centre, and on the comparisons
between the simulated orbits in Yukawa gravity and two independent sets of
observations. Our simulations resulted in strong constraints on the range of
Yukawa interaction and showed that its most probable value in the
case of S2 star is around 5000 - 7000 AU. At the same time, we were not able to
obtain reliable constrains on the universal constant of Yukawa
gravity, because the current observations of S2 star indicated that it may be
highly correlated with parameter in the range . For
they are not correlated. However, the same universal constant
which was successfully applied to clusters of galaxies and rotation curves of
spiral galaxies () also gives a satisfactory agreement with the
observed orbital precession of the S2 star, and in that case the most probable
value for the scale parameter is AU. Also, the
Yukawa gravity potential induces precession of S2 star orbit in the same
direction as General Relativity for and for , and in
the opposite direction for . The future observations with
advanced facilities, such as GRAVITY or/and European Extremely Large Telescope,
are needed in order to verify these claims.Comment: 16 pages, 8 figures, accepted for publication in JCA
Constraints on gravity from precession of orbits of S2-like stars
We study some possible observational signatures of gravity at Galactic
scales and how these signatures could be used for constraining this type of
gravity. For that purpose, we performed two-body simulations in
gravity potential and analyzed the obtained trajectories of S2-like stars
around Galactic center, as well as resulting parameter space of gravity
potential. Here, we discuss the constraints on the gravity which can be
obtained from the observations of orbits of S2-like stars with the present and
next generations of large telescopes. We make comparison between the
theoretical results and observations. Our results show that the most probable
value for the parameter in gravity potential in the case of S2-like
stars is 100 AU, while the universal parameter is close to 0.01.
Also, the gravity potential induces the precession of S2-like stars orbit
in opposite direction with respect to General Relativity, therefore, such a
behavior of orbits qualitatively is similar to a behavior of Newtonian orbits
with a bulk distribution of matter (including a stellar cluster and dark matter
distributions).Comment: 12 pages, 12 figures, accepted in Phys. Rev.
Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds
Recently, the LIGO-Virgo collaboration discovered gravitational waves and in
their first publication on the subject the authors also presented a graviton
mass constraint as eV (Abbott et al., 2016).
In the paper we analyze a potential to reduce upper bounds for graviton mass
with future observational data on trajectories of bright stars near the
Galactic Center. Since gravitational potentials are different for these two
cases, expressions for relativistic advance for general relativity and Yukawa
potential are different functions on eccentricity and semimajor axis, it gives
an opportunity to improve current estimates of graviton mass with future
observational facilities. In our considerations of an improvement potential for
a graviton mass estimate we adopt a conservative strategy and assume that
trajectories of bright stars and their apocenter advance will be described with
general relativity expressions and it gives opportunities to improve graviton
mass constraints. In contrast with our previous studies, where we present
current constraints on parameters of Yukawa gravity (Borka et al., 2013) and
graviton mass (Zakharov et al., 2016) from observations of S2 star, in the
paper we express expectations to improve current constraints for graviton mass,
assuming the GR predictions about apocenter shifts will be confirmed with
future observations. We concluded that if future observations of bright star
orbits during around fifty years will confirm GR predictions about apocenter
shifts of bright star orbits it give an opportunity to constrain a graviton
mass at a level around eV or slightly better than current
estimates obtained with LIGO observations.Comment: 16 pages, 1 Figure, 1 Table, corrected minor typo
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