Galaxy-Sized Observatory for Gravitational Waves

Sep 17, 2009 by Lin Edwards weblog
Artist's impression of a gravitational wave. Image: NANOGRAV

(PhysOrg.com) -- Astronomers are making plans to create a galaxy-sized observatory to look for gravitational waves. The project is part of a joint effort with astronomers from Australia and Europe, who also aim to try to detect gravitational waves.

Astronomers are making plans to create a galaxy-sized observatory to look for . The project is part of a joint effort with from Australia and Europe, who also aim to try to detect gravitational waves.

Einstein's general predicts the existence of gravitational waves, which are usually described as ripples in space-time produced by masses, rather as a boat produces waves in water as it travels. Gravitational waves pass through matter and their strength weakens as they travel away from their source. The effect of the waves is to cause incredibly tiny fluctuations in the distance between the observer and the source.

Gravitational waves have not yet been detected directly in practice (although they have been shown to exist by indirect means). It should theoretically be possible to detect them through minute disturbances in the time that light or radio waves take to travel from the source in space to an observer.

The new project has been proposed by a consortium of astronomers known as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). The proposal is to study the radio waves from pulsars to identify these disturbances, which should be detectable as fluctuations in the times of arrival of the radio pulses. In effect, the pulsars seem to shimmer as the waves wash over them. They described their proposal in a submission by F. Jenet et al. to the Astro2010 Program Prioritization Panel on Particle Astrophysics and Gravitation earlier this month.

At present, a precision of <100 ns in timing is achieved for only the most measured pulsars, but within the next decade or so astronomers believe improvements in instruments and reductions in signal-noise ratios, along with advancements such as the square kilometer array to be built in Australia or South Africa, could mean they would be able to study a 'pulsar timing array'ť (PTA) consisting of about 100 pulsars, with a timing precision of <100 ns for each pulsar in the network.

NANOGrav proposes that constant observation of such a PTA would enable them to observe gravitational waves in the nanohertz to microhertz band, as well as other phenomena such as supermassive black holes and radiation relics from phenomena originating in the early stages of the universe's evolution, such as inflation and cosmic strings and superstrings.

The array of pulsars would in effect form a galactic-sized , which would be the most revolutionary advance in astronomy since Galileo's time.

More information:

arxiv.org/abs/0909.1058
www.nanograv.org/

via Technology Review

© 2009 PhysOrg.com

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User comments : 14

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deatopmg
1 / 5 (15) Sep 17, 2009
Since gravity travels more than 100,000,000 times faster than light (by measurement and by calculation) how will any detected waves (IMO - unlikely) be associated with known objects?
Mr_Frontier
5 / 5 (3) Sep 17, 2009
Measurement and calculation, please. Also, why do you think it's unlikely to be detected with any known objects? Where are you coming from and where are you going?
JES
5 / 5 (4) Sep 17, 2009
Gravity travels at the speed of light
Alexa
Sep 17, 2009
This comment has been removed by a moderator.
Alexa
2.6 / 5 (5) Sep 17, 2009
Gravity travels at the speed of light

This is highly unlikely in analogy to water surface, where surface waves are playing role of light waves and underwater sound waves correspond gravitational waves (which are way way faster). This analogy explains too, why we didn't observe gravitational waves already, while ignoring CMB noise.

BTW This post was deleted from here due the alleged "absence of reference", although no reference is required for posts in "Comments Guidelines".

http://www.physor...comments

Anyway, superluminal gravity models are quite common in peer-reviewed journals.

http://arxiv.org/.../0604154
http://arxiv.org/abs/0806.1167
axemaster
4 / 5 (4) Sep 17, 2009
"This is highly unlikely in analogy to water surface, where surface waves are playing role of light waves and underwater sound waves correspond gravitational waves (which are way way faster). This analogy explains too, why we didn't observe gravitational waves already, while ignoring CMB noise."

Actually, it's quite certain that gravity travels at exactly the speed of light. One need merely observe the orbits of the planets to prove that - the orbits are very slightly offset as a result of the time delay. This was one of the biggest proofs of general relativity. Another process is the gravitomagnetic effect, which is in the process of being proven as we speak.

And don't make some silly analogy, it is unnecessary and highly misleading, especially since the one you used is completely wrong. Surface waves are entirely different, because they are 2D, and light is 3D.
axemaster
5 / 5 (2) Sep 17, 2009
"Since gravity travels more than 100,000,000 times faster than light (by measurement and by calculation) how will any detected waves (IMO - unlikely) be associated with known objects?"

Where did you come up with that number? Do you have any idea what that would imply in terms of relativity? For example, none of our GPS satellites would work if gravity was at that speed. Plus, the entire basis for the "speed of light" has to do with the universe's spacetime unit calculation speed. To say that gravity can move faster than light is completely illogical.

Plus, as I already stated, there is considerable direct evidence showing the speed of gravitational propagation = c. If you say "they can't know that", then I would remind you of the fame a physicist would achieve if he proved it wrong. They have tried very hard in testing this.
Alexa
2.3 / 5 (3) Sep 17, 2009
..Surface waves are entirely different, because they are 2D, and light is 3D...

Of course, water surface is just an illustrative low-dimensional model of real situation. Vacuum is composed of quantum foam and the light is spreads along (mem)branes (surface gradients) of this foam in transversal waves. Whereas gravitational waves can spread across sparse interior of "quantum foam bubbles", which enables them to propagate in much weaker but much faster way.

Concerning gravitational waves and relativity, even prof. Einstein wasn't convinced proponent of gravitational waves. Now, after fifty years we still have no direct observational evidence of these waves available. I'd recommend you to become familiar with Einstein's objections, if you don't believe in my analogies. If nothing else, it's interesting history of peer-reviewed science.

http://blogs.disc...l-review
http://dafix.uark...eree.pdf
Alexa
1 / 5 (1) Sep 17, 2009
...none of our GPS satellites would work if gravity was at that speed....
It's easy to say, but how can you explain it? It means, when I say: "no - it's not true" - how can you prove your stance? Maybe you're right, but I don't see any logical evidence for it.
Alexa
1 / 5 (1) Sep 17, 2009
..one need merely observe the orbits of the planets to prove that - the orbits are very slightly offset as a result of the time delay..
Perihelion precession of Mercury and Venus isn't related to radiation of gravitational waves, but frame dragging effect. For a system like the Sun and Earth the power radiated by GW's is just a 200 watts. The only (indirect) evidence of gravitational waves is the decrease of rotation period in result of gravitational field dispersion.
Alexa
1 / 5 (1) Sep 17, 2009
Illustratively speaking: rotation of Mercury precession can be arbitrarily high - but until Mercury will encircle Sun with the same frequency, it's evident, no gravitational waves were radiated outside of solar system, so no direct evidence of such waves can be given there.

And because gravitational waves should disperse during their traveling through bubbles of quantum foam, even at the case, when such braking really occurs we cannot be sure, we will detect some gravitational waves at larger distance.
Alexa
not rated yet Sep 17, 2009
..gravitomagnetic effect, which is in the process of being proven as we speak..
The only finished experiment to measure gravitomagnetic effects is the Gravity Probe B spaceprobe, which failed completely in this point.

In the data for the frame-dragging results presented, the random errors were much larger than the theoretical expected value and scattered on both the positive and negative sides, therefore causing skepticism on whether any useful data could be extracted in the future to test this effect.
sender
not rated yet Sep 17, 2009
Surprised that cascading photon interferometry analysis hasn't rooted out gravity wave generation or propagation in smart fluid environments yet.
Alexa
not rated yet Sep 17, 2009
BTW Pulsars are distributed across Galaxy at distances of many hundred light years. If scientists are expecting, gravitational waves spread in luminal speed, it would mean, some perturbations resulting from gravitational wave would exhibit delays in scale of years from quasar to quasar. Such measurement would have meaning only when highly superluminal speed of gravitational waves is considered.
Velanarris
Sep 18, 2009
This comment has been removed by a moderator.
Velanarris
Sep 18, 2009
This comment has been removed by a moderator.
jamesrm
not rated yet Sep 19, 2009
"(although they have been shown to exist by indirect means)"

Shouldn't that be "inferred to exist" it sound like they are scared to admit any fallibility.

Even they find something with this galaxy sized observatory it will still only be indirect evidence.

Regards
James
Alexa
Sep 19, 2009
This comment has been removed by a moderator.
Alexa
Sep 19, 2009
This comment has been removed by a moderator.
Alexa
Sep 19, 2009
This comment has been removed by a moderator.