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Post Info TOPIC: Gravity Waves
Blobrana


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Chiral gravity
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Gravity's bias for left may be written in the sky

Is gravity left-handed? An answer could provide a clue to a long-sought theory of quantum gravity - and might be within our grasp by 2013.
General relativity describes gravity's actions at large scales. For tiny scales however, a theory of quantum gravity, incorporating quantum mechanics, is needed. But first physicists need to understand gravitons, hypothetical quantum particles that mediate the gravitational force. These likely come in left and right-handed varieties: in the former, the particle's spin would be aligned with the direction of its motion; in the latter, the spin would be the opposite.
General relativity does not distinguish between right and left, so you might expect gravity to be transmitted by both varieties. But the quantum world may play favourites. When it comes to the ghostly particles known as neutrinos, for example, the weak force only interacts with the left-handed variety.
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Blobrana


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Posts: 131433
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Gravitons
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Title: Chirality in unified theories of gravity
Authors: F. Nesti, R. Percacci
(Version v2)

We show how to obtain a single chiral family of an SO(10) GUT, starting from a Majorana-Weyl representation of a unifying ("GraviGUT") group SO(3,11), which contains the gravitational Lorentz group SO(3,1). An action is proposed, which reduces to the correct fermionic GUT action in the broken phase.

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Blobrana


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Posts: 131433
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Gravitational wave sources
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Study predicts distribution of gravitational wave sources

A pair of neutron stars spiralling toward each other until they merge in a violent explosion should produce detectable gravitational waves. A new study led by an undergraduate at the University of California, Santa Cruz, predicts for the first time where such mergers are likely to occur in the local galactic neighbourhood.
According to Enrico Ramirez-Ruiz, associate professor of astronomy and astrophysics at UC Santa Cruz, the results provide valuable information for researchers at gravitational-wave detectors, such as the Laser Interferometry Gravitational-Wave Observatory (LIGO) in Louisiana and Washington.
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Blobrana


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RE: Gravity Waves
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Title: The Distribution of Coalescing Compact Binaries in the Local Universe: Prospects for Gravitational-wave Observations.
Authors: Luke Zoltan Kelley, Enrico Ramirez-Ruiz, Marcel Zemp, Jürg Diemand and Ilya Mandel

Merging compact binaries are the most viable and best-studied candidates for gravitational-wave (GW) detection by the fully operational network of ground-based observatories. In anticipation of the first detections, the expected distribution of GW sources in the local universe is of considerable interest. Here we investigate the full phase-space distribution of coalescing compact binaries at z = 0 using dark matter simulations of structure formation. The fact that these binary systems acquire large barycentric velocities at birth ("kicks") results in merger site distributions that are more diffusely distributed with respect to their putative hosts, with mergers occurring out to distances of a few Mpc from the host halo. Redshift estimates based solely on the nearest galaxy in projection can, as a result, be inaccurate. On the other hand, large offsets from the host galaxy could aid the detection of faint optical counterparts and should be considered when designing strategies for follow-up observations. The degree of isotropy in the projected sky distributions of GW sources is found to be augmented with increasing kick velocity and to be severely enhanced if progenitor systems possess large kicks as inferred from the known population of pulsars and double compact binaries. Even in the absence of observed electromagnetic counterparts, the differences in sky distributions of binaries produced by disparate kick-velocity models could be discerned by GW observatories, within the expected accuracies and detection rates of advanced LIGO - in particular with the addition of more interferometers.

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Blobrana


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Can the Similarity between Gravitation and Electromagnetism Be Exploited?

If the sign of a successful scientific theory is that you get more out of it than you put in, then the most successful of all must be Einstein's general theory of relativity. Starting from a few simple principles and earthy thought experiments, such as what would happen if you got stuck in a falling elevator, general relativity predicts everything we know about gravity and much we never suspected. In the latest example, John Swain of Northeastern University suggests that it might be possible to build a gravitational transformer that transfers kinetic energy just as an electrical transformer transfers electrical energy.
The idea is based on the uncanny resemblance between the equations of general relativity and those of electricity and magnetism. The gravitational attraction that makes apples fall is analogous to an electric field, with mass playing the role of electric charge. And just as the motion of electric charges gives rise to a magnetic field, so the motion of mass gives rise to a "gravitomagnetic" field. Earth's spin, for instance, tugs on satellites in an effect known as frame dragging.
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Blobrana


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Is the universe a big hologram? This device could find out.

During the hunt for the predicted ripples in space-time - known as gravitational waves - physicists stumbled across a rather puzzling phenomenon. Last year, I reported about the findings of scientists using the GEO600 experiment in Germany. Although the hi-tech piece of kit hadnt turned up evidence for the gravitational waves it was seeking, it did turn up a lot of noise.
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Blobrana


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PIRE project
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New project will use pulsars to detect gravitational waves

With a recently announced $6.5 million grant over five years from the National Science Foundation (NSF), an international consortium of researchers and institutions hopes to find and use the galaxy's most precise pulsars as tools for detecting gravitational waves.
The project, funded under the Partnership for International Research and Education (PIRE) program, will use telescopes around the world, including the Cornell-managed Arecibo Observatory, to survey and monitor the sky for millisecond pulsars. (Pulsars are rapidly spinning neutron stars that emit lighthouse-like beams of radio waves.)
By monitoring the pulsars over five or more years, the researchers hope to find evidence of gravitational waves through tiny perturbations in the spacing of the pulsars' beams.
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Blobrana


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RE: Gravity Waves
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Correcting for rotational instabilities of pulsars, the most precise clocks in the Universe

An international team of astronomers, including Michael Kramer from the Max-Planck-Institut für Radioastronomie (Bonn, Germany) has studied the behaviour of natural cosmic clocks and discovered a way to potentially turn them into the best time keepers in the Universe. The scientists made their breakthrough using decade-long observations from the 76-m Lovell radio telescope at the University of Manchester's Jodrell Bank Observatory to track the radio signals of an extreme type of star known as a pulsars. This new understanding of pulsar spin-down could improve the chances to use the fastest spinning pulsars in order to make the first direct detection of ripples, known as gravitational waves, in the fabric of space time.
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Blobrana


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Getting the drop on gravity

Gravity is mercilessly impartial - on Earth, it accelerates light and heavy objects alike with a tug of 9.8 metres per second squared. That property is the cornerstone of Albert Einstein's theory of general relativity, which states that gravity is indistinguishable from any other type of acceleration. But some physicists wonder whether gravity's tug might be fractionally different on objects of different mass, or whether it might change its behaviour at short distances - such as those at which the rules of quantum mechanics come into play.
The problem is that any deviation would be miniscule. Current experiments, which use twisting pendulums or precise laser measurements of the changing distance between Earth and the Moon, can detect incredibly small variations in gravity's expected tug. So far, no changes have been seen.
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Blobrana


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Posts: 131433
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Gravitational Waves
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Probing the dark side of the universe

Advancing into the next frontier in astrophysics and cosmology depends on our ability to detect the presence of a particular type of wave in space, a primordial gravitational wave. Much like ripples moving across a pond, these waves stretch the fabric of space itself as they pass by. If detected, these weak and elusive waves could provide an unprecedented view of the earliest moments of our universe. In an article appearing in the May 21 issue of Science, Arizona State University theoretical physicist and cosmologist Lawrence Krauss and researchers from the University of Chicago and Fermi National Laboratory explore the most likely detection method of these waves, with the examination of cosmic microwave radiation (CMB) standing out as the favoured method.
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