Warped spacetime around BH and the barycenter

[Robittybob1]

This is interesting

 

In electrodynamics, circular polarization of an electromagnetic wave is a polarization in which the electric field of the passing wave does not change strength but only changes direction in a rotary manner.

So if there is any connection to how GW work the passing GW would not change strength but only direction and that would make my statement quoted in #61 possibly true.

I think time will tell. Let's take a break.

Sorry - I have just realised that this is the thread I have moderated in; I thought that was the other one. I can participate or moderate - not both; I should step away from this thread. Apologies

I'm also going to take a break and step away for a while.

[Strange]

Please, how do you define orbital plane? Define the angle of inclination of the orbital plane to the line of sight.

 

I am not defining anything (although I'm sure the meaning of orbital plane is pretty obvious: the plane that they are orbiting in).

 

Note that (as you have seen in some other simulations) if the black holes are spinning then there can be precession and the orbital plane will change orientation. For this reason, the paper defines the angle very carefully - I don't have it to haand at the moment, but I seem to remember that they took the value at a particular orbital rate (20Hz?). The graph in the paper shows that the most likely angle between the normal to the plane (which they define as the vector of angular momentum) is about 150 degrees. So 30 degrees off perpendicular to the plane.

General relativity is used, I agree, but once the waves are in space traveling at the speed of light why can't we revert to general physics after that?

 

Because the waves only exist in GR.

[Robittybob1]

http://arxiv.org/pdf/1602.03840v1.pdf

"The posterior PDF shows that an orientation of the total orbital angular momentum of the BBH strongly misaligned to the line of sight is disfavoured; the probability that 45◦ < θJN < 135◦ is 0.35."

 

Orbital angular momentum is orthogonal to the orbital plane is that correct?

So they say the chances (probability) of it being a side on view are not favoured. For the angles of total angular momentum as the range only occur with a somewhat side on view. Is that the correct interpretation of that sentence from the paper?

 

@Strange - Reading your post we are now on the same page as they say.

 

When they give the outcome in a measure of probability one can't rule out the opposite being true in some cases.

 

There are some nice traces of the LIGO detection, very spread out Fig 6 page 10/19.

 

I am not defining anything (although I'm sure the meaning of orbital plane is pretty obvious: the plane that they are orbiting in).

 

Note that (as you have seen in some other simulations) if the black holes are spinning then there can be precession and the orbital plane will change orientation. For this reason, the paper defines the angle very carefully - I don't have it to hand at the moment, but I seem to remember that they took the value at a particular orbital rate (20Hz?). The graph in the paper shows that the most likely angle between the normal to the plane (which they define as the vector of angular momentum) is about 150 degrees. So 30 degrees off perpendicular to the plane.

 

Because the waves only exist in GR.

"So 30 degrees off perpendicular to the plane." Do you mean "the orbital plane was 60 degrees to the line of sight"

That could mean we are looking at it from underneath in a manner of speaking.

[Robittybob1]

 

.....

Because the waves only exist in GR.

I think one of the best explanations for the difference between relativity (GR) and Newtonian gravity is the following paragraph from the paper:

 

 

In general relativity, two objects in orbit slowly spiral

together due to the loss of energy and momentum through

gravitational radiation [4, 5]. This is in contrast to Newtonian

gravity where bodies can follow closed, elliptical

orbits [6, 7]. As the binary shrinks, the frequency and amplitude

of the emitted GWs increase. Eventually the two

objects merge. If these objects are BHs, they form a single

perturbed BH that radiates GWs at a constant frequency

and exponentially damped amplitude as it settles to its final

state [8, 9].

I was surprised by this statement:

 

 

The results are based on a complete analysis of the data surrounding this event. The only information from the search-stage is the time of arrival of the signal.

I wonder when they can tell when the signal first arrived? For when I put a ruler across the tops of the waves the Hanford strain trace lasts longer than the Livingston one yet the peaks seem to be earlier in the Hanford site at the beginning of the signal. This might be part of the issue with superimposing wave signals as I was explaining in #66, where in different regions of space the signals will form nodes and others regions not as much. This suggests a more top/bottom or even an intermediary line of sight rather than a true side on view.

The time domain data covers a period of just over 0.2 seconds.

The observed time delay 6.9 ms:

 

 

The observed time-delay of GW150914 between the Livingston

and Hanford observatories was 6.9

+0.5

−0.4 ms

Are they saying the signal arrived in Livingston first? Are they using the largest peak to take these times from? How can they pick up when the signal started when the reading is virtually flat?

.

[Strange]

When they give the outcome in a measure of probability one can't rule out the opposite being true in some cases.

 

The probability of some orientations is pretty much zero.

 

 

That could mean we are looking at it from underneath in a manner of speaking.

 

What does "underneath" mean?

 

 

Are they saying the signal arrived in Livingston first? Are they using the largest peak to take these times from? How can they pick up when the signal started when the reading is virtually flat?

 

I'm sure these questions are answered in one of the other papers describing the details of the detection and analysis. My guess would be that they used some sort of correlation function to determine the time difference. Looking at a single peak would not be very accurate.

[Robittybob1]

 

The probability of some orientations is pretty much zero.

 

 

What does "underneath" mean?

 

 

I'm sure these questions are answered in one of the other papers describing the details of the detection and analysis. My guess would be that they used some sort of correlation function to determine the time difference. Looking at a single peak would not be very accurate.

Didn't someone use the word "above" so "beneath" is below that!

What I was thinking was that these BBHs had been producing G-waves for the last million years or so how can you identify when the signal starts, but there was a definite maximum peak and that followed by the ringdown.

If you see the paper that mentions how they established the timing please post it.

Edited March 15, 2016 by Robittybob1

[swansont]

The observed time delay 6.9 ms:

 

The signal travels at c, so that corresponds to about 2,000 km. How far apart are the observatories? (edit: 3,002 km) That would give the maximum time delay you'd expect. You can reconstruct where the event is by applying some trig. The uncertainties in the arrival time will mean this isn't a point, but a region.

 

If there was no delay, you'd have two possible answers, in opposite directions.

 

edit:

Being 3000 km apart means the delay could be up to 10 ms.

[Strange]

If you see the paper that mentions how they established the timing please post it.

 

It is here: http://arxiv.org/abs/1602.03839

 

You can find a helpful index and overview of the papers here: http://cplberry.com/2016/02/23/gw150914-the-papers/ (which is how I found that one)

[Robittybob1]

 

The signal travels at c, so that corresponds to about 2,000 km. How far apart are the observatories? (edit: 3,002 km) That would give the maximum time delay you'd expect. You can reconstruct where the event is by applying some trig. The uncertainties in the arrival time will mean this isn't a point, but a region.

 

If there was no delay, you'd have two possible answers, in opposite directions.

 

edit:

Being 3000 km apart means the delay could be up to 10 ms.

So if I understand you if the line of site was directly above Hanford (H) and Livingston (L) the two signals would possibly arrive at the same time, but since H and L are separated by around 2000 km and L gets the signal first the signal came from somewhere on a line of sight looking from the general direction of H to L?

 

2 directions "two possible answers" because the waves will go through the Earth as well.

Edited March 15, 2016 by Robittybob1

[swansont]

So if I understand you if the line of site was directly above Hanford (H) and Livingston (L) the two signals would possibly arrive at the same time, but since H and L are separated by around 2000 km and L gets the signal first the signal came from somewhere on a line of sight looking from the general direction of H to L?

 

2 directions "two possible answers" because the waves will go through the Earth as well.

 

 

If the signal was from above, I don't think you'd register a signal, because the test masses don't oscillate in those directions. In fact, the two LIGO sites are aligned to each other as much as possible so that they are both sensitive to events.

 

http://arxiv.org/pdf/1404.5623v5.pdf

 

any source that lies in the plane of zero time delay between the detectors is always localized to two opposite patches. Because the HL detectors were placed nearby (at continental rather than intercontinental distances) on the surface of the Earth so as to keep their arms nearly coplanar, their combined network antenna pattern has two maxima that lie on opposite sides of that great circle. As a consequence, a large fraction of sources are localized to two islands of probability that cannot be distinguished based on time or amplitude on arrival.

[Robittybob1]

 

It is here: http://arxiv.org/abs/1602.03839

 

You can find a helpful index and overview of the papers here: http://cplberry.com/2016/02/23/gw150914-the-papers/ (which is how I found that one)

.Bit of a goose chase so far and I'm still unsure. From the above link I got:

 

 

The difference in time of arrival between the Livingston and

Hanford detectors from the individual triggers in the PyCBC

analysis is 7.1ms, consistent with the time delay of 6.9

+0.5

−0.4 ms

recovered by parameter estimation [18]

From that footnote link led me to

 

http://arxiv.org/pdf/1602.03840v1.pdf

 

 

The observed time delay, and the need for the registered

signal at the two sites to be consistent in amplitude

and phase, allow us to localize the source to a ring on the

sky [34, 35]. Where there is no precession, changing the

viewing angle of the system simply changes the observed

waveform by an overall amplitude and phase. Furthermore,

the two polarizations are the same up to overall amplitude

and phase. Thus, for systems with minimal precession, the

distance, binary orientation, phase at coalescence and sky

location of the source change the overall amplitude and

phase of the source in each detector, but they do not change

the signal morphology. Phase and amplitude consistency

allow us to untangle some of the geometry of the source. If

the binary is precessing, the GW amplitude and phase have

a complicated dependency on the orientation of the binary,

which provides additional information.

The observed time-delay of GW150914 between the Livingston

and Hanford observatories was 6.9

+0.5

−0.4 ms. With

only the two LIGO instruments in observational mode,

GW150914’s source location can only be reconstructed

to approximately an annulus set to first approximation

by this time-delay [103, 104].

.Looking at that 103, 104 footnote: Gave background work on using the time delay.

.

 

 

If the signal was from above, I don't think you'd register a signal, because the test masses don't oscillate in those directions. In fact, the two LIGO sites are aligned to each other as much as possible so that they are both sensitive to events.

 

http://arxiv.org/pdf/1404.5623v5.pdf

 

any source that lies in the plane of zero time delay between the detectors is always localized to two opposite patches. Because the HL detectors were placed nearby (at continental rather than intercontinental distances) on the surface of the Earth so as to keep their arms nearly coplanar, their combined network antenna pattern has two maxima that lie on opposite sides of that great circle. As a consequence, a large fraction of sources are localized to two islands of probability that cannot be distinguished based on time or amplitude on arrival.

That reads a bit like a "treasure map" when reading "to two islands of probability that cannot be distinguished". I'm not sure whether GW on some lines of sight can't be detected.

 

There will always be two islands for there are those waves coming in from above the plane of the detectors and below. Above and below no matter from which direction.

Defining some terms:

GW150914

I suppose that is Gravity Wave 2015, Sept 09 and 14th day ... GW 15/09/14 >>> GW150914

PyCBC

 

PyCBC is a python toolkit for analysis of data from gravitational-wave laser interferometer detectors with the goal of detecting and studying signals from compact binary coalescences (CBCs).

Edited March 15, 2016 by Robittybob1

[swansont]

 

That reads a bit like a "treasure map" when reading "to two islands of probability that cannot be distinguished". I'm not sure whether GW on some lines of sight can't be detected.

 

There will always be two islands for there are those waves coming in from above the plane of the detectors and below. Above and below no matter from which direction.

 

 

 

There would not be two islands if they detectors were sensitive to signals from any direction. There would be a ring of possibilities. No delay means the source is equidistant, and that defines a circle. "Above and below no matter from which direction" is a self-contradicting statement. Above and below are specific directions.

 

In the section before the one I previously quoted:

"Significant misalignment would have created patches of the sky that were accessible to one detector but in a null of the other detector’s antenna pattern, useless for a coincidence test. "

 

So they say flat-out detectors have regions where they can't detect a signal. Now you can be sure of this.

[Robittybob1]

 

 

There would not be two islands if they detectors were sensitive to signals from any direction. There would be a ring of possibilities. No delay means the source is equidistant, and that defines a circle. "Above and below no matter from which direction" is a self-contradicting statement. Above and below are specific directions.

 

...

What I was trying to say in my layman way was that there is a sort of a plane created by the horizon and there is above and below that horizontal plane, but there is also the 360 degree rotation (that is the "no matter which direction" bit). From that I say "Above and below (the horizontal plane) and no matter from which direction (on the 360 degree rotation)"

You might have a more concise way of saying that?

 

I see they use the term "tangent to the Earth's surface" for my horizontal plane.

 

 

.

 

In the section before the one I previously quoted:

"Significant misalignment would have created patches of the sky that were accessible to one detector but in a null of the other detector’s antenna pattern, useless for a coincidence test. "

 

So they say flat-out detectors have regions where they can't detect a signal. Now you can be sure of this.

https://dcc.ligo.org/public/0109/P1300187/023/ms.pdf

 

 

Figure 5 explains it.

 

 

Shading indicates the RMS network antenna pattern, with darker areas corresponding to high sensitivity and white

corresponding to null sensitivity

Edited March 15, 2016 by Robittybob1

[swansont]

What I was trying to say in my layman way was that there is a sort of a plane created by the horizon and there is above and below that horizontal plane, but there is also the 360 degree rotation (that is the "no matter which direction" bit). From that I say "Above and below (the horizontal plane) and no matter from which direction (on the 360 degree rotation)"

You might have a more concise way of saying that?

 

 

It's moot because it's wrong. They quote clearly say that for zero time delay there are two regions where the source can be. I don't care what your reasoning is, the conclusion contradicts the paper.

[Robittybob1]

 

 

If the signal was from above, I don't think you'd register a signal, because the test masses don't oscillate in those directions. In fact, the two LIGO sites are aligned to each other as much as possible so that they are both sensitive to events.

 

....

It was this statement that did not seem to fit into what was displayed in Fig 5. Do you still stand by "if the signal was from above, I don't think you'd register a signal"? From the discussion I thought the opposite was true.

 

When I said "Above and below no matter from which direction." I'm only describing where the GWs could be coming from. Basically meaning from all directions but according to figure 5 a BBH directly above the LIGO will be equidistant and sensitive to detection.

Edited March 15, 2016 by Robittybob1

[swansont]

It was this statement that did not seem to fit into what was displayed in Fig 5. Do you still stand by "if the signal was from above, I don't think you'd register a signal"? From the discussion I thought the opposite was true.

 

When I said "Above and below no matter from which direction." I'm only describing where the GWs could be coming from. Basically meaning from all directions but according to figure 5 a BBH directly above the LIGO will be equidistant and sensitive to detection.

 

 

I was forgetting about the transverse nature of the waves, so I was wrong about that. But it just moves the null point 90 degrees. So there's still two regions.

[Robittybob1]

 

 

I was forgetting about the transverse nature of the waves, so I was wrong about that. But it just moves the null point 90 degrees. So there's still two regions.

Yes that how I understand it too now. Thanks.