Actually there are lots of gravitational waves; we just haven’t detected them directly yet. The LIGO and VIRGO collaborations have put their heads together — over 700 authors! — and come up with the best limit yet on gravitational waves from inspiralling massive black-hole binaries.
Search for gravitational waves from binary black hole inspiral, merger and ringdown
The LIGO Scientific Collaboration, the Virgo Collaboration (722 authors)
(Submitted on 18 Feb 2011)
We present the first modeled search for gravitational waves using the complete binary black hole gravitational waveform from inspiral through the merger and ringdown for binaries with negligible component spin. We searched approximately 2 years of LIGO data taken between November 2005 and September 2007 for systems with component masses of 1-99 solar masses and total masses of 25-100 solar masses. We did not detect any plausible gravitational-wave signals but we do place upper limits on the merger rate of binary black holes as a function of the component masses in this range. We constrain the rate of mergers for binary black hole systems with component masses between 19 and 28 solar masses and negligible spin to be no more than 2.0 per Mpc^3 per Myr at 90% confidence.
Note the caveats on the analysis: for one thing, it’s looking for the inspiral phase in particular (which should be the easiest to see). More importantly, they’re looking for a specific mass range — between 25 and 100 solar masses total in the binary system, which is rather large. (But nicely positioned for LIGO’s frequency sensitivity.) And of course they’re looking for black holes, not neutron stars (which would be less massive).
The truth is, they shouldn’t have seen anything, according to our best theoretical estimates. From the conclusions:
We did not detect any plausible gravitational-wave candidates. However we estimated our search sensitivity and were able to constrain the merger rate of the targeted sources in the nearby Universe. We established to 90% confidence that the merger rate of black holes with component masses between 19Msun and 28Msun is less than 2.0 Mpc-3 Myr-1. We note that this is still about an order of magnitude higher than optimistic estimates for such systems [28] (see also [13, 19])
So, keep looking. They’re getting closer; the next step is to upgrade to Advanced LIGO. Once that happens, a lack of detections will be more surprising than actually detecting something.
My understanding is that negligible spin is probably a very unlikely thing, too–when I’ve seen the astrophysicists estimate $frac{a}{M}$ parameters, I don’t remember seeing anything smaller than something like $0.2$.
NO SUSY NO GRAV WAVES == MISERY
No (detectable) SUSY + no (detectable) gravitational waves = pretty much what lots of people were expecting at this stage.
Oh, this was sort of my idea at one point, this version is more simple and focus on one thing in particular. My version of this had more to do with seperating gravity from a black hole from naturally occuring gravity in any particular system your measuring. Which is sort of like this. But not really. Then again what the hell is naturally occuring gravity?
If you keep on banging your heads against walls, you might just break one. Hoorah!
Sorry people there is no such thing as gravity…the world sucks.
But you can see it. The speed of the galactic black hole at the center of sprial galaxies should leave a wake or, a gravity well. If you focus on the outer rims of any spiral galaxy photograph the galactic center has a noticeable depression from the rim to the center of the galaxy. Please keep in mind that the slight depression has to be measured in light years.
Sorry people there is no such thing as gravity…the world sucks.
But you can see it. The speed of the galactic black hole at the center of most galaxies should leave a wake or, a gravity well. If you focus on the outer rims of any sprial galaxy photograph you will see a noticeable depression from the rim to the center of the galaxy. Would be interesting if a red shift could confirm this as the direction of travel.
LIGO is now what – at least 20 years old, if not 25?
Indeed, can’t wait for Advanced LIGO!
But Sean, this search is _not_ for inspiral-only signals: as hinted in the title, this is the first search that used full waveforms created by merging analytical inspiral computations, fits to numerical-relativity mergers, and ringdown waveforms from black-hole perturbation theory. These hybrids are by no means perfect, and they don’t include spin effects, but they do extend how far the search can see, by looking for the extra energy emitted in the merger and ringdown.
@valatan: true that, but even signals computed for nonspinning systems would do pretty well at matching spinning sources. That is to say, this search _would_ have seen moderately spinning sources if they had been close enough.
@Joseph: the mass of the central black hole is actually quite negligible compared to the rest of the galaxy, although locally it can make for nice fireworks. But no big wake as you suggest, unfortunately.
@Arun: LIGO’s “first lock” (the analog of first light for telescope) was at the end of 2000, but it only reached its design sensitivity in 2005. And even after that, it only performed science runs for something like two years of triple coincidence (all three detectors on). So it’s not like it’s been looking for 20 years.
Way back when, I took a general relativity course offered through the math department of the university I went to. It was much harder than special relativity. The math was daunting. It took a long time to get through the tensor algebra and tensor calculus. But still, the significance of the quantifies expressed in the tensor form, the usage of dual spaces, etc., essentially eluded me, as did the meaning of the field equations, until I worked through the one problem that was directly soluble that I knew of, the Schwarzschild solution. (There were chapters on gravity waves and cosmological metrics as well.)
What gets me though is when I read the Wikipedia article on solutions to the Einstein field equations, it reads like a foreign language; no mention is made of the Schwarzschild solution per se, except a for it as a ‘vacuum solution’, which is a misleading classification to the uninitiated reader if you ask me. What’s written there is fairly inaccessible to me and although it might serve a purpose to experts and savants (does it?), it should not be so confoundedly general or abstract. It, like many other math related articles, start from a high level of abstraction and never seem to descend to the masses of interested readers like myself. I suppose that clicking on ‘Schwarzschild vacuum’ gives you the way to solve the field equation, but linking from hard, abstract, and for pros only pages to simpler and descriptive pages for anyone it is not a good way to link articles.
Anyway, at the time I took the course, I was rather amazed at the prediction of gravity waves, although now I’m not. In retrospect, I should have seen that it is utterly natural and necessary for waves to exist in something analogous to a fabric that can be warped and twisted. So here’s hoping for Advanced LIGO.
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As Eddington pointed out already before many years, gravitational waves do not have a unique speed of propagation. The speed of the alleged waves is coordinate dependent. A different set of coordinates yields a different speed of propagation and such waves would propagate like noise. From AWT perspective the detection of gravitational waves is like the attempt to observe longitudinal waves of particle environment with these transverse ones.
The same result can be imagined easily with water surface model, where transverse waves are serving like the analogy of waves of light and the gravitational waves are behaving like longitudinal sound waves, which are spreading through underwater. Because sound waves are spreading a way faster, then the surface waves, they would manifest like indeterministic noise at the water surface – and no expensive analysis or devices is required for such understanding…
Relativists use a simplified form of Einstein’s field equations to calculate various properties of his gravitational field, including gravitational waves, which are based on the Einstein’s pseudo-tensor. This simplified form is called the linearised field equations. They do this because field equations are highly non-linear (implicit actually) and impossible to solve analytically. So they use the linearised form, simply assuming that they can do so. However Hermann Weyl proved in 1944 already, that linearisation of the field equations implies the existence of a Einstein’s pseudo-tensor that, except for the trivial case of being precisely zero, does not otherwise exist:
http://www.jstor.org/stable/2371768
In another words, the alleged gravitational waves are the consequence of simplification of field equations and they have nothing to do with physical reality. They’re solely an artefact of incomplete formal model used and this fact is known for more than one half of century already.
Life will be a bit more interesting if there is ever robust gravitational wave astronomy. Still yet to reach the “confirm existing predictions” stage.
Sean, there are no *guaranteed* astrophysical sources even for advanced LIGO.
(LISA of course has)
LIGO has to be unique among modern “big-science” experiments as it was designed and built knowing full well it almost certainly would not see ANYTHING! What are the odds, in 5 years of so, of Advanced LIGO, seeing exactly the same nothing? It’s absolutely amazing that any government would fund such an expensive fundamental project with so long a “pay-back” time.
Zephir,
How then do you explain the orbital decay of Hulse-Taylor binary pulsar ?
What are the expectations and how are they derived? Is there are more fruitful way to look?
What does a merger rate denote? It is hard to tell if it refers to the implicit strength of the G constant or some feature of gravity waves themselves. Normally I would think it was talking about strength of gravitational attraction.
If we didn’t expect LIGO and VIRGO to have the power to detect gravity waves in anywhere near the range that theory predicted, why did we bother launching those projects? It seems a bit like building a telescope to look at the next valley over in the bottom of your own valley instead of at the top of the hill because it is too much work to climb the hill.
Some Observations of my own. Sort of like referees in college basketball are portrayed as infallible saints by telecasters, so too with Everthing I have ever read about LIGO (modulo a small political criticism about the WA & LA site selections). The technology, developed at MIT & Caltech, was rock-solid by all reviews, including NSF’s; hence the first 280M$$, (approx. 1/40 the cost of the SSC) was doled w/out so much as the blink of an eye almost 20 yrs ago.
Naturally. It had the halo of Einstein’s creation, & in `1974, a binary pulsar was measured by Hulse & Taylor to be spinning down precisely at the rate GR predicted for grav wave emission. Everything seemed to be, in basketball parlance, a `SlamDunk’: GR’s predix of grav waves seemed to be an inevitable discovery, just waiting to happen.
However, after ~ a decade, as one science run after another was published with Null results, we got suspicious, but were told to keep the faith, & that `advanced’ LIGO would save the day.
But really, will it ? Why was LIGO built in the first place: A test bed for Adv. LIGO ??
That is not how I recall the sales pitch. It’s almost like the `fall-back’ position of the SUSY proponents, who will never accept reality & clamor for the ILC to vindicate them. One upmanship seems to be the norm.
Meanwhile GEO600 seems to have preliminary evidence for a noise source traceable to the Planck scale, sufficiently solid that Argonne labs is now building a dedicated interferometer, a `holometer’, to nail it down precisely. Would’nt it be spookily ironic if the grav wave antennas, built like `pyramids in the desert’ as monuments to classical gravity theory, inadvertently found the empirical basis for quantum gravity instead ? Einstein would turn over in his grave if he had one.
As I recall, LIGO and Advanced LIGO were actually “sold” honestly, that they had little chance of detecting anything (essentially zero for LIGO). That’s the most remarkable thing about the project, from an outsider’s viewpoint. It’s the only really expensive pure science project I can think of for which this has been true.
You know right away that they didn’t find anything – papers titled “A Search for…” always mean the answer is negative…
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Well, we spent a quarter of a century in love with string theory, guess our new sweetheart will be gravity waves. Even tho nothing to support it.