202 research outputs found
Pioneer's Anomaly and the Solar Quadrupole Moment
The trajectories of test particles moving in the gravitational field of a
non-spherically symmetric mass distribution become affected by the presence of
multipole moments. In the case of hyperbolic trajectories, the quadrupole
moment of an oblate mass induces a displacement of the trajectory towards the
mass source, an effect that can be interpreted as an additional acceleration
directed towards the source. Although this additional acceleration is not
constant, we perform a general relativistic analysis in order to evaluate the
possibility of explaining Pioneer's anomalous acceleration by means of the
observed Solar quadrupole moment, within the range of accuracy of the observed
anomalous acceleration. We conclude that the Solar quadrupole moment generates
an acceleration which is of the same order of magnitude of Pioneer's constant
acceleration only at distances of a few astronomical units.Comment: Typos corrected, references adde
Matching conditions in relativistic astrophysics
We present an exact electrovacuum solution of Einstein-Maxwell equations with
infinite sets of multipole moments which can be used to describe the exterior
gravitational field of a rotating charged mass distribution. We show that in
the special case of a slowly rotating and slightly deformed body, the exterior
solution can be matched to an interior solution belonging to the Hartle-Thorne
family of approximate solutions. To search for exact interior solutions, we
propose to use the derivatives of the curvature eigenvalues to formulate a
matching condition from which the minimum radius can be derived at which
the matching of interior and exterior spacetimes can be carried out. We prove
the validity of the matching in the particular case of a static mass with
a quadrupole moment. The corresponding interior solution is obtained
numerically and the matching with the exterior solution gives as a result the
minimum radius of the mass configuration
Multipole structure of compact objects
We analyze the applications of general relativity in relativistic
astrophysics in order to solve the problem of describing the geometric and
physical properties of the interior and exterior gravitational and
electromagnetic fields of compact objects. We focus on the interpretation of
exact solutions of Einstein's equations in terms of their multipole moments
structure. In view of the lack of physical interior solutions, we propose an
alternative approach in which higher multipoles should be taken into account
Quasi-homogeneous black hole thermodynamics
Although the fundamental equations of ordinary thermodynamic systems are
known to correspond to first-degree homogeneous functions, in the case of
non-ordinary systems like black holes the corresponding fundamental equations
are not homogeneous. We present several arguments, indicating that black holes
should be described by means of quasi-homogeneous functions of degree different
from one. In particular, we show that imposing the first-degree condition leads
to contradictory results in thermodynamics and geometrothermodynamics of black
holes. As a consequence, we show that in generalized gravity theories the
coupling constants like the cosmological constant, the Born-Infeld parameter or
the Gauss-Bonnet constant must be considered as thermodynamic variables
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