Exciting news: Gravitational Waves detected!

Are low-frequency continuous gravitational waves a sign for pending binary black hole mergers, contrary to the "chirp" encountered at the actual event?

Alex.

If BeatleJuice goes supernova in our lifetime, would we be able to detect gravitational waves from that event?

Not too close or the high energy radiation will fry us.

The estimated safe distance is 50-100 light years, and Betelgeuse is over 600 ly away, this wiki article has some interesting details.

There is of course the possibility of a two faint white dwarfs or neutron stars in a nearby close binary that we can't see... spiralling away, and E@H discovers them via gravity wave search! I can see the headlines now "E@H predict a mass extinction event"

Hallo!
Also my congratulations to this extraordinary results and event!

I´ve just some small questions to the results:
I red the paper from B.P. Abbott et. al.. On page 2, fig. 1 are shown the reconstructed signals from both detectors. Easily one can see the differences in the reconstructed waveforms between both detectors, especially during the time of merging of the two BHs. (I´d plot this from the published data.) According to Fig. 3a in the paper, the detectors are twisted by about 20° only.
Now my questions: Does this differences in amplitude result from the polarisation of the GW? Or is this only due to the increasing phaseshift with increasing frequency and varying amplitude between both detectors due to their long geometrical separation? In the list of estimated source parameters is nothing said about polarisation. Presumably it needs at minimum one more widely separated detector to dig out the polarisation of the wave + or x from all the data.

Kind regards and happy crunching
Martin

Time for a question:
A hot object radiates away energy with photons

Does a mass radiate away energy with gravitons? If so, what is left?

Yes, I know gravity is so weak this will take a long time.

Fabulous. They obviously had someone assigned to article a fair number of weeks ago, and got lots of the players to talk to them.

I thought they handled the delicate problem of what to say about Joseph Weber well.

The 2 black holes merging have radiated away 3 solar masses, because the mass of the final black hole is 3 solar masses less than the sum of the 2 masses.
Tullio

Congratulations, very exciting news! I can't wait to crunch units from the new run.

AFAIK a mass sitting still does not emit gravitational waves. It does only if it is accelerated. The same thing happens to charged particles, they emit radiation when accelerated like electrons in a synchrotron which emit radiation (synchrotron light).
Tullio

I've checked on a book by Peter G.Bergmann, "The riddle of gravitation" whose Italian edition I have edited. He says:
Gravitational waves are emitted by massive bodies subjected to an acceleration and travel at the speed of light.
Prof.Bergmann was a coworker of Einstein.
Tullio

Gravity is the weakest of the four basic interactions but it is the more important at great distances.It manages planets, stars, and galaxies and also dark matter, as is evidenced by the deflection on light beams coming from distant objects if there is a massive object, also made by darkmatter, in the foreground. This is called the Einstein lens and has been demonstrated by observing several images of the same supernova arriving at different times depending on the light paths. The gravitational constant G, also called the Newton constant, has been measured in different ways and there is an international effort to measure it with greater accuracy. The Lisa Pathfinder spacecraft, now orbiting the L1 Lagrange point, might be used to measure it, according to ESA.
Tullio

I think there is a difference between static fields and dynamic fields. A massive object has a static field and can bend space-time. This action was considered a force in Newton times, now in Einstein times one does not speak of forces. Naturally it is easier to think of forces than of a warped space-time and we all do it in practice, even if it no longer correct.
A dynamic field results from an accelerated mass. It is also pictured as a force, and this gives the familiar pictures of centrifugal forces. Far easier than speaking of gravitational waves emitted by the accelerated mass. A gravity force is the equivalent of a constant accelerated system, as in the gedanken experiment. If an elevator is accelerated upwards in a gravity free space, the person in the elevator thinks he is subjected to a gravity force. I am very interested in the Lisa Pathfinder experiment where two masses will be freed in a gravity free space at the Lagrange point. Presumably they will attract each other and this will give the opportunity to measure the G constant of gravitational force.
A steady electric current running through a wire produces a magnetic field but it is a static field. Only if the current is alternating, at the frequency of 50 or 60 Hz, it will produce an electromagnetic wave of that frequency. Once at the University I put my finger to the input of an oscilloscope set at 50 Hz and I saw a sine wave on its display. My body was acting as a collector of electromagnetic waves. The magnetic field of a common magnet is a static field.
Tullio

I have cited a book by Peter G. Bergmann. He says that GWs are produced by an accelerated mass. If a mass travels at constant speed,as in special relativity, it will not produce GW. A static mass neither.
Tullio

Additional...

Tullio, thanks for having recalled me some basics !
I can hardly be foregiven to have forgot them.
I take an example you gave in a previous post that I should have read with more attention : statics never create waves (electromagnetics for instance).
Thanks again.
JF

Isn't everything in our universe constantly accalerated? The mass may seem to sit still in the shelf, but for sure it is accelarated relatively to any other frame of reference. Hence, it should emit gravitational waves.

edit: Didn't read the previous post. It think we try to make the same point.

Well, the kilo (together with the shelf and the earth) is rotating around the sun. If I remember correctly this is a kind of acceleration because the vector of the speed is constantly changing. So the kilo (together with the shelf and the earth) should emit gravitational waves.

Amazing, because 200W is so minimal! No wonder gravity waves are hard to detect!

It has to be a particular pattern of acceleration to emit waves : non-axisymmetric. This is code for (a) not a simple injection of extra mass (b) not a simple displacement. The technical word is quadripolar or higher mode. For example if a star expanded and contracted in radius only, but evenly all over it's surface, then no GW's arise. It is conservation of mass/energy that prevents a monopolar pattern, and conservation of momentum that prevents a bipolar pattern.

In the case of the Earth going around the Sun think of it like a very uneven barbell. The axis of rotation is close to the heavier end of the barbell and as the Earth progresses around the Sun the motion is 'non-axially symmetric'.

{ Now IF the axis of rotation was the line joining the centers of the Earth and Sun ( which it isn't ) then that would be 'axially symmetric' and hence produce no GW's }

The other example of special interest at E@H is 'mountains' on neutron stars. These low bumps - but containing alot of mass - sit out from the general spherical shape. So it is like an unevenly balanced spin cycle in the clothes washer, but we can't stop it to distribute the wet clothes more evenly around the bowl ! This will radiate GW's and we hope one day to detect that.

Cheers, Mike.

( edit ) In generality ( very very Back Of The Envelope here ! ) one ought consider a given system with respect to G/c^2 ie. Newton's gravitational constant divided by light speed squared. In MKS units that is 6.67 * 10^[-11]/(3 * 10^[8])^2 ~ 10^[-27]. So you need objects of order 10^[30] kg ( the Sun ) and/or velocities of the order of light speed to get a decent measurable effect as well as moving in the above pattern.

You will note that as c -> infinity ( Newton's instantaneous transmission of gravity ) then G/c^2 -> zero ie. no waves. If gravity was stronger ( increase G ) or the speed of light was less ( decrease c ) then we'd see these GW's more routinely without the need for the really fancy gadgets. On useful way of thinking of any field ( gravitational or other ) is for the transmission of effects, rather like the legendary cheque being 'in the mail' where for a short time at least neither sender nor receiver has actual custody of the money. With those fast moving black holes there was a lot of funds in transit .... :-)

I remember reading a long time ago about the possibility of 'millimeter mountains' on neutron stars. We might perhaps know if they exist or not when we, here at E@H, detect what we are looking for - continuous GW. I imagine such 'mountains' would be a possible source. Without detecting the GW, how would you ever be able to 'see' them or even be sure they existed?

So, keep searching, even if you don't understand why :-).

Mike, I think you have mixed up there and given the answer for what we could detect and not the field itself.

Consider an electromagnetic field. We get radio from frequencies > 0. However a frequency of zero also changes the field, but only when it is established or ends. Mathematically it is a translation. So just like when you put AC into an antenna and transmit a signal, if you put DC into an antenna you also transmit a signal (permanent magnet). Of course if the remote observer doesn't happen to catch it when it starts, he won't know it is there as there is no absolute frame he can compare to. Kind of like us here on earth, we can only tell which way Earth's pole is, we don't know where the galactic pole is until we get our compass needle away from earth.

The same applies to the gravitational field. If you create a mass you have warped space time. Half of a square wave which propagates out at c. Unless the distant observer was watching at the time you created it he won't know because there is no absolute frame to refer to.

Thinking about this a bit more, a single mass moving at a constant velocity in the universe should warp space time, but there is no frame of reference to measure it against, except itself. To perform a measurement (real not thought) you have to introduce a second mass and as soon as you do the two masses will accelerate towards each other.

Perhaps the result here is that all frames of reference in the real world are accelerating frames of reference and there is no rest frame. Actually that seems to agree well with my understanding of relativity.

Now as G is such a dang small constant, yes it takes huge masses being offset to launch a wave that will have enough power when it gets here to earth to be above the noise floor. But that is engineering, not physics. In physics a virtual particle pair involved in Hawking radiation creates a gravitational wave.
posted before I saw your touche

Hallo!
Yesterday Karsten Danzmann (director of AEI Hannover) answered in an interview for a major local newspaper (Der Tagesspiegel) on the question: “Why do you need so many detectors, isn´t just one sufficient?†“Each of them is omnidirectional, that means, he registers signals from all directions and can´t distinguish the polarization, the direction of oscillation. With two of them one can fairly reconstruct the direction of the source, with three that works better, but is unable to distinguish between up and down. Only with a minimum of 4 detectors one can gather the total signal in regard of direction and polarization.â€
By the way: From Google Maps data one can learn that in regard to Livingston Hanford is twisted by 81° clockwise, looking from above, and tilted by nearly 33° due to the curvature of the earth surface, taking the earth as a perfect ball.

Kind regards and happy crunching
Martin

Sure, but that depends upon your degree of approximation to symmetry. One could reasonably model the Earth as having uniform density, or at least has the only interesting variation dependent purely on the radial distance ( onion like ), or furthermore features only related to displacement from the axis of rotation. If so the Earth's rotation won't produce GW's. Now if you want to care about the uniqueness of Mt Everest say, then some miniscule radiation will occur ( best of luck measuring that ).

Maybe a gas giant planet would be more like it. Their lack of solidity ought preclude any lasting non-axisymmetry, but that depends on how sure you are of the interior.

If you are thinking of systems with some number of discrete bodies then you'd have to come up with something pretty strange. Not impossible, just unlikely to form naturally. Hmmmm. Hang on. Accretion discs form frequently enough, so how many of those are suitably arranged ? Again it comes back to how close to pure symmetry you want which in turn ( upper ) bounds any radiation ....

Try Larry Niven's Ringworld ? Or alternatively just play Halo. :-)

Cheers, Mike.

Thanx a lot Mike.
My question was quite unclear, sorry.
It concerned only the theoretical possibilities to have somewhere a non quadripolar (or more) system in our common universe (not talking of worm holes or multivers).
Take for example Jove. It has satellites which from time to time are in conjunction. Then, its shape is distorted (a little) because of the mass of its satellites and Jove is no longer perfectly spherical.
The Moon tides on earth must have the same effect and I guess that it is the same elsewhere.

I agree that the result in terms of GW is not measurable at the moment (and maybe for ever !) but I remain convinced that we live in a swimming pool of GW.
That we can catch them or not was not my question.
The proof of existence is a thing, the proof of non existence is an other thing.
Am I wrong ?

Ah. Yes. These waves of whatever magnitude abound. Most are irrelevant in that far, far larger magnitude affects dominate.

All science is contingent. Even the best efforts and theories may suffer contradiction by reality tomorrow. Often that leads not to total refutation of a set of ideas but refinement or bounding of applicability. Not detecting GW's was a possible outcome and as such ( with sufficient confidence in technique/execution etc ) would have lead to a re-frame of theory. GW's were detected and so people have hailed the experiment as a success, but it would also have been a success if we were correctly informed that GW's don't occur. A good experiment doesn't validate precepts. A good experiment tells you what nature is, not what you'd like it to be. In generality this is a heavily misunderstood foundation of science, and much confusion flows downstream because.

{ The second most misunderstood aspect of science is that any theory has a realm of applicability defined by it's assumptions. Hence one ought not complain that semiconductor lattice wave functions fail to predict anything useful in stellar cores. }

Cheers, Mike.