14,570 research outputs found
Searching for continuous gravitational wave sources in binary systems
We consider the problem of searching for continuous gravitational wave
sources orbiting a companion object. This issue is of particular interest
because the LMXB's, and among them Sco X-1, might be marginally detectable with
2 years coherent observation time by the Earth-based laser interferometers
expected to come on line by 2002, and clearly observable by the second
generation of detectors. Moreover, several radio pulsars, which could be deemed
to be CW sources, are found to orbit a companion star or planet, and the
LIGO/VIRGO/GEO network plans to continuously monitor such systems. We estimate
the computational costs for a search launched over the additional five
parameters describing generic elliptical orbits using match filtering
techniques. These techniques provide the optimal signal-to-noise ratio and also
a very clear and transparent theoretical framework. We provide ready-to-use
analytical expressions for the number of templates required to carry out the
searches in the astrophysically relevant regions of the parameter space, and
how the computational cost scales with the ranges of the parameters. We also
determine the critical accuracy to which a particular parameter must be known,
so that no search is needed for it. In order to disentangle the computational
burden involved in the orbital motion of the CW source, from the other source
parameters (position in the sky and spin-down), and reduce the complexity of
the analysis, we assume that the source is monochromatic and its location in
the sky is exactly known. The orbital elements, on the other hand, are either
assumed to be completely unknown or only partly known. We apply our theoretical
analysis to Sco X-1 and the neutron stars with binary companions which are
listed in the radio pulsar catalogue.Comment: 31 pages, LaTeX, 6 eps figures, submitted to PR
The gravitational Vavilov-Cherenkov effect
In this essay we show that an uncharged black-hole moving superluminally in a
transparent dielectric medium violates Hawking's area theorem. The violation is
overcome through the emission of radiation. Since modes cannot emerge from the
black hole itself, this radiation must originate from a collective effect in
the medium, in complete analogy with the Vavilov-Cherenkov effect. However,
because the black-hole is uncharged, the emission mechanism must be different.
We discuss the physical origin of the effect and obtain a Newtonian estimative.
Then we obtain the appropriate equations in the relativistic case and show that
the field which is radiated away is a combination of gravitational and
electromagnetic degrees of freedom. Possible astrophysical relevance for the
detection of primordial black-holes and binary systems is discussed.Comment: 9 pages, Honorable Mention from the Gravity Research Foundation, 199
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