196 research outputs found

### Generation of Post-Newtonian Gravitational Radiation via Direct Integration of the Relaxed Einstein Equations

The completion of a network of advanced laser-interferometric
gravitational-wave observatories around 2001 will make possible the study of
the inspiral and coalescence of binary systems of compact objects (neutron
stars and black holes), using gravitational radiation. To extract useful
information from the waves, such as the masses and spins of the bodies,
theoretical general relativistic gravitational waveform templates of extremely
high accuracy will be needed for filtering the data, probably as accurate as
$O[(v/c)^6]$ beyond the predictions of the quadrupole formula. We summarize a
method, called DIRE, for Direct Integration of the Relaxed Einstein Equations,
which extends and improves an earlier framework due to Epstein and Wagoner, in
which Einstein's equations are recast as a flat spacetime wave equation with
source composed of matter confined to compact regions and gravitational
non-linearities extending to infinity. The new method is free of divergences or
undefined integrals, correctly predicts all gravitational wave ``tail'' effects
caused by backscatter of the outgoing radiation off the background curved
spacetime, and yields radiation that propagates asymptotically along true null
cones of the curved spacetime. The method also yields equations of motion
through $O[(v/c)^4]$, radiation-reaction terms at $O[(v/c)^5]$ and
$O[(v/c)^7]$, and gravitational waveforms and energy flux through $O[(v/c)^4]$,
in agreement with other approaches. We report on progress in evaluating the
$O[(v/c)^6]$ contributions.Comment: 11 pages, PTPTeX, submitted to Proceedings of the Yukawa-Kyoto
International Seminar 9

### The 1919 measurement of the deflection of light

The measurement of the deflection of starlight during a total solar eclipse
on May 29, 1919 was the first verification of general relativity by an external
team of scientists, brought Einstein and his theory to the attention of the
general public, and left a legacy of experimental testing that continues today.
The discovery of gravitational lenses turned Einstein's deflection into an
important tool for astronomy and cosmology. This article reviews the history of
the 1919 measurement and other eclipse measurements, describes modern
measurements of the effect using radio astronomy, and of its cousin, the
Shapiro time delay, and discusses gravitational lenses.Comment: 17 pages, 3 figures. Submitted to Classical and Quantum Gravity for
its "Milestones of General Relativity" focus issue to be published during the
Centenary Year of G

### Resource Letter PTG-1: Precision Tests of Gravity

This resource letter provides an introduction to some of the main current
topics in experimental tests of general relativity as well as to some of the
historical literature. It is intended to serve as a guide to the field for
upper-division undergraduate and graduate students, both theoretical and
experimental, and for workers in other fields of physics who wish learn about
experimental gravity. The topics covered include alternative theories of
gravity, tests of the principle of equivalence, solar-system and binary-pulsar
tests, searches for new physics in gravitational arenas, and tests of gravity
in new regimes, involving astrophysics and gravitational radiation.Comment: 9 pages; submitted to American Journal of Physic

### Orbital flips in hierarchical triple systems: relativistic effects and third-body effects to hexadecapole order

We analyze the secular evolution of hierarchical triple systems in the
post-Newtonian approximation to general relativity. We expand the Newtonian
three-body equations of motion in powers of the ratio $a/A$, where $a$ and $A$
are the semimajor axis of the inner binary's orbit and of the orbit of the
third body relative to the center of mass of the inner binary, respectively.
The leading order "quadrupole" terms, of order $(a/A)^3$ relative to the
$1/a^2$ acceleration within the inner binary, are responsible for the
well-known Kozai-Lidov oscillations of orbital inclination and eccentricity.
The octupole terms, of order $(a/A)^4$ have been shown to allow the inner orbit
to "flip" from prograde relative to the outer orbit to retrograde and back, and
to permit excursions to very large eccentricities. We carry the expansion of
the equations of motion to hexadecapole order, corresponding to contributions
of order $(a/A)^5$. We also include the leading orbital effects of
post-Newtonian theory, namely the pericenter precessions of the inner and outer
orbits. Using the Lagrange planetary equations for the orbit elements of both
binaries, we average over orbital timescales, obtain the equations for the
secular evolution of the elements through hexadecapole order, and employ them
to analyze cases of astrophysical interest. We find that, for the most part,
the orbital flips found at octupole order are robust against both relativistic
and hexadecapole perturbations. We show that, for equal-mass inner binaries,
where the octupole terms vanish, the hexadecapole contributions can alone
generate orbital flips and excursions to very large eccentricities.Comment: 16 pages, 11 figures, typos corrected; matches published versio

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