Gravitational lens and gravitational waves question

[Robittybob1]

But with GE each pass of the half of the binary produces another positive wave so I think the frequency of the GE wave will be twice the orbital frequency. So if it was liken to bow waves it would be two speed boats chasing each other in a circle and each time they come close to you a bow wave would travel toward you. But we are dealing with 3 dimensional space rather than a water surface so it is possible the waves are all around rather than just like ripples on a pond.

http://www.scienceforums.net/topic/93472-gravitational-lens-and-gravitational-waves-question/page-2#entry909493 could well be right.

Edited March 5, 2016 by Robittybob1

[swansont]

Was that a joke?

 

 

No. Which part did you think was a joke? The non-isotropy of the radiation, or the astrophysicist?

Was the quote from her twitter feed? I would be surprised if that was right. Why do you think it was sensible? I would love to know the right answer.

 

Yes. I asked the question on twitter. That was her response.

 

Why the surprise? She has a PhD in astrophysics so she's been studying (and understanding) this stuff for years.

 

In EM radiation, a dipole or quadrupole has a particular radiation pattern, which is not isotropic. No reason for me to think gravitational radiation would behave differently.

[Robittybob1]

 

 

No. Which part did you think was a joke? The non-isotropy of the radiation, or the astrophysicist?

 

Yes. I asked the question on twitter. That was her response.

 

Why the surprise? She has a PhD in astrophysics so she's been studying (and understanding) this stuff for years.

 

In EM radiation, a dipole or quadrupole has a particular radiation pattern, which is not isotropic. No reason for me to think gravitational radiation would behave differently.

That was the first time I've seen a twitter post used in that way on a science forum. I looked up her credentials. I came around after a while. #26

Edited March 5, 2016 by Robittybob1

[Strange]

GE production slows the body allowing the orbit to decay, so if it is removing force that was directed tangentially to the orbit I thought the energy given off would be an expression of this lost energy i.e at all times it is generating a wave front to the fore and these waves spread out from there.

Like a bow wave of a boat maybe.

 

Calculating the gravitational waves generated by the merger of black holes requires massively complicated simulations using supercomputers. So I wouldn't put too much faith in your guesses, if I were you.

From Katie Mack's page, I was eventually led to this: http://cplberry.com/2016/02/23/gw150914-the-papers/

 

An excellent, and really useful, summary of all the papers around the LIGO result. There are papers that go into great detail about every aspect: the detection, modelling the sources, etc. This is a great way to find the ones that are of interest.

Edited March 5, 2016 by Strange

[swansont]

But with GE each pass of the half of the binary produces another positive wave

 

It does?

[Robittybob1]

 

It does?

At least in most of the animations it does. Look at the image at 1:38 on the MIT video.

 

 

Logically it would, for do you think it wouldn't? I'm trying to think of how. If both orbiting BHs or stars had the same mass, why wouldn't they both have the same contribution? I must admit it is harder to see when the masses are out of balance like the Sun-Earth for you don't get the effect of the Sun sweeping past you. It still must be there though.

So were you thinking in terms of just the one wave per orbit for the system as a whole?

How does that logic go?

[Strange]

At least in most of the animations it does.

 

You are confusing a 2D cartoon with the physics of space-time.

Edited March 5, 2016 by Strange

[Robittybob1]

 

You are confusing a 2D cartoon with the physics of space-time.

Well what happens in reality then? How would you answer Swansont's question in #30?

[swansont]

At least in most of the animations it does. Look at the image at 1:38 on the MIT video.

 

Logically it would, for do you think it wouldn't? I'm trying to think of how. If both orbiting BHs or stars had the same mass, why wouldn't they both have the same contribution? I must admit it is harder to see when the masses are out of balance like the Sun-Earth for you don't get the effect of the Sun sweeping past you. It still must be there though.

So were you thinking in terms of just the one wave per orbit for the system as a whole?

How does that logic go?

I'm not interested in the logic, I'm interested in the science. You're guessing, based on an animation, but phrasing it as if it's known science. You need to stop doing that.

 

The "logic" is that in EM interactions, the frequency of the emitted radiation is the frequency difference of the states. With in antenna, if you drive it at some frequency, you get that frequency of radiation. Now, maybe there are cases where you get twice that value. What I want is confirmation based on physics. Animations might look the way they do because it looks good, not because it reflects the underlying physics.

Well what happens in reality then? How would you answer Swansont's question in #30?

It wouldn't come up, because Strange likely wouldn't have made the claim without actually knowing it was valid.

[Robittybob1]

I'm not interested in the logic, I'm interested in the science. You're guessing, based on an animation, but phrasing it as if it's known science. You need to stop doing that.

 

The "logic" is that in EM interactions, the frequency of the emitted radiation is the frequency difference of the states. With in antenna, if you drive it at some frequency, you get that frequency of radiation. Now, maybe there are cases where you get twice that value. What I want is confirmation based on physics. Animations might look the way they do because it looks good, not because it reflects the underlying physics.

 

It wouldn't come up, because Strange likely wouldn't have made the claim without actually knowing it was valid.

I am trying to answer you. When they got that "chirp" do you think the frequency they got had nothing to do with the orbital period? I did, so maybe I'm mistaken.

The way I imagined it was happening was that the frequency increased as the orbital period decreased as the binary BH orbits decayed rapidly in the last half second.

(I am not basing my concept on the animation, but MIT must have chosen that animation therefore we can presume it tries to explain the situation.)

 

I am trying to answer you. When they got that "chirp" do you think the frequency they got had nothing to do with the orbital period? I did, so maybe I'm mistaken.

The way I imagined it was happening was that the frequency increased as the orbital period decreased as the binary BH orbits decayed rapidly in the last half second.

(I am not basing my concept on the animation, but MIT must have chosen that animation therefore we can presume it tries to explain the situation.)

 

Yet looking into a bit further the animation that was shown along with the announcement there was not always 2 waves per rotation.

It was harder to see the relationship. It starts at 4:50 into the clip https://www.youtube.com/watch?v=n5Ycv2yYNG8 which was "a computer simulation using Einstein's equations.

Looking closer at it there was a period where there were two waves per revolution for a while from about 5:05 - 5:10.

Edited March 5, 2016 by Robittybob1

[swansont]

I am trying to answer you. When they got that "chirp" do you think the frequency they got had nothing to do with the orbital period? I did, so maybe I'm mistaken.

The way I imagined it was happening was that the frequency increased as the orbital period decreased as the binary BH orbits decayed rapidly in the last half second.

 

No, I think the frequency has everything to do with the orbital period. I haven't said anything to the contrary. But you stated something specific, as if you had certainty, and you don't have that certainty.

 

The proper answer to my question would have been an admission that you don't actually know. That you overstated the claim.

[Robittybob1]

No, I think the frequency has everything to do with the orbital period. I haven't said anything to the contrary. But you stated something specific, as if you had certainty, and you don't have that certainty.

 

The proper answer to my question would have been an admission that you don't actually know. That you overstated the claim.

Do the edits I made on #35 help?

If as you say it is related to the orbital period, is it just the decision as to whether it is 2 pulses or just 1 per orbit that you are considering or are there other ratios that are possible?

Edited March 5, 2016 by Robittybob1

[swansont]

Do the edits I made on #35 help?

If as you say it is related to the orbital period, is it just the decision as to whether it is 2 pulses or just 1 per orbit that you are considering or are there other ratios that are possible?

If I knew, I would not have asked for confirmation of your claim. I would have either refuted you or said nothing, as appropriate.

[Strange]

The way I imagined it was happening ...

 

Calculating the gravitational waves generated by the merger of black holes requires massively complicated simulations using supercomputers. So I wouldn't put too much faith in your guesses, if I were you.

 

(I thought it worth repeating.)

[Robittybob1]

 

Calculating the gravitational waves generated by the merger of black holes requires massively complicated simulations using supercomputers. So I wouldn't put too much faith in your guesses, if I were you.

 

(I thought it worth repeating.)

Thanks. Those simulations would need certain conditions put on the programs at the beginning. Someone would have had to decide whether there were 1,2, 3, 4 .... waves per orbit. That is one of the first steps and that is all we are deciding here. I chose 2 because each body of the binary is emitting the gravitational energy separately. They are both falling toward each other leading to the merger.

Edited March 5, 2016 by Robittybob1

[StringJunky]

Thanks. Those simulations would need certain conditions put on the programs at the beginning. Someone would have had to decide whether there were 1,2, 3, 4 .... waves per orbit. That is one of the first steps and that is all we are deciding here. I chose 2 because each body of the binary is emitting the gravitational energy separately. They are both falling toward each other leading to the merger.

I could well be wrong, but I understood the production of GWs started at the point of complete merger. This is point where there has been a change in mass, you need this to produce them. To me, it follows then, that there is only one object producing one set of waves, the waves from the new and bigger blackhole, the short period the merger is completing... that's that spiky bit in the signal. This is that Caltech LIGO video again:

 

[Robittybob1]

 

I could well be wrong, but I understood the production of GWs started at the point of complete merger. This is point where there has been a change in mass, you need this to produce them. To me, it follows then, that there is only one object producing one set of waves, the waves from the new and bigger blackhole, the short period the merger is completing... that's that spiky bit in the signal. ...

 

Well I could be wrong too.

That wiggly line at the bottom is the GW passing through the LIGO. This tells me that GE is being radiated long before the last -0.75 secs.

I have not worked out how it happens but BHs still have gravity so "gravitons" seem to be able to go out of the BH even if other types of radiation can't. So if it was gravitons being lost as GWs or GE and this allows the BHs to fall and speed up (the orbital period collapses) both orbiting at a smaller radius, I can just about see how a BH can lose mass long before the merger.

I would prefer to see it described by the researchers themselves but that is how I'm thinking about it ATM.

(There are 2 waves per orbit - comparing the wiggly line to the orbits of the BHs)

The "logic" is that in EM interactions, the frequency of the emitted radiation is the frequency difference of the states. With in antenna, if you drive it at some frequency, you get that frequency of radiation. Now, maybe there are cases where you get twice that value. What I want is confirmation based on physics. Animations might look the way they do because it looks good, not because it reflects the underlying physics.....

if I understand your analogy correctly could there be two drivers sharing the same antenna 180 degrees out of phase, and then only producing rectified positive waves? (Gravity can only attract) The sinusoidal look of the GW is really only positive wave crests falling down to zero, rather than a true positive and negative phases of the sinusoidal curve.

Now that might seem really hard to take but could it be the case?

Edited March 6, 2016 by Robittybob1

[Strange]

Thanks. Those simulations would need certain conditions put on the programs at the beginning. Someone would have had to decide whether there were 1,2, 3, 4 .... waves per orbit.

 

No they wouldn't. That would come out of the equations of general relativity that are being simulated. The initial conditions would be things like the masses of the black holes, their spins and distances.

[Mordred]

trust me the Nbody codes is a bugger to correlate to the Einstein field equations. However Strange is correct, the paper I posted earlier this thread has some of the applicable mathematics. I have two N-body textbooks and even though I know the formulas involved. I can't even get past chapter one of either book and I can program in over 20 programming lanquages. (just a side note lol)

 

http://arxiv.org/pdf/gr-qc/0309058v2.pdf

Edited March 6, 2016 by Mordred

[Robittybob1]

 

No they wouldn't. That would come out of the equations of general relativity that are being simulated. The initial conditions would be things like the masses of the black holes, their spins and distances.

Spins - as in rotation rate of the black hole? What type of spins are you talking about?

Distances - do you mean orbital radius, the orbital radius went from extremely large right down to a total merge. So what difference would distance have? Exactly what distance are you meaning?

Would the masses make any difference to the number of wavefronts per orbit? How would that have an effect?

Do you think you could vary the number of wavefronts per orbit by varying the balance of the BH masses?

 

They know the frequency of the "chirp" So if there is only 1 wavefront per orbit the binary is orbiting at twice the rate of the system that had 2 wavefronts per orbit. There have been estimates of the final tangential speeds of the BHs, and we should be able to calculate the size of their event horizons so we should be able to tell from those estimates if there were two or one wave per orbit.

Edited March 6, 2016 by Robittybob1

[Mordred]

 

I have not worked out how it happens but BHs still have gravity so "gravitons" seem to be able to go out of the BH even if other types of radiation can't. So if it was gravitons being lost as GWs or GE and this allows the BHs to fall and speed up (the orbital period collapses) both orbiting at a smaller radius, I can just about see how a BH can lose mass long before the merger.

I would prefer to see it described by the researchers themselves but that is how I'm thinking about it ATM.

 

 

 

You wouldnt see gravity emitted from inside the BH, The mass is lost from the EH photon sphere outward. The only way a BH can lose mass is via Hawking radiation. Think of it this way the information of the mass inside the EH is stored at the photon sphere.

[Robittybob1]

 

 

You wouldnt see gravity emitted from inside the BH, The mass is lost from the EH photon sphere outward. The only way a BH can lose mass is via Hawking radiation. Think of it this way the information of the mass inside the EH is stored at the photon sphere.

How are you defining the photon sphere? That from memory was 3/2 times the radius of the EH. You say "the mass is lost from the EH photon sphere outward", is that the region between the EH and the photon sphere? Or still further out?

"binary black hole mergers.pdf " http://w.astro.berkeley.edu/~gmarcy/astro160/papers/binary_black_hole_mergers.pdf covers quite a lot of interesting detail.

[Mordred]

its [latex]3/2 R_s[/latex] where [latex] R_s[/latex] is the Schwartzchild radius. Yeah I mean't EH not the photon sphere. Overtired lol

[Strange]

Spins - as in rotation rate of the black hole?

 

Exactly. Note that a black hole is fully characterized by just three things (the no hair theorem): mass, electric charge, and angular momentum.

 

Form the link I posted earlier:

"We’re currently working on results using a waveform that includes the full effects of spin, but that is extremely slow (it’s about half done now), so those results won’t be out for a while."

http://cplberry.com/2016/02/23/gw150914-the-papers/#parameter-estimation

That was written in February, about 6 months after the detection. That should give you an idea of how complex these simulations are.

 

 

Distances - do you mean orbital radius, the orbital radius went from extremely large right down to a total merge.

 

Yes.

 

So what difference would distance have?

 

There is no simple answer to that. But the closer they get, the faster the orbits.

 

There is a probably more accurate, and nicely annotated, simulation here: http://cplberry.com/2015/09/12/monty-carla/

[swansont]

Here's the kind of confirmation I was looking for

http://www.physics.usu.edu/Wheeler/GenRel2013/Notes/GravitationalWaves.pdf

 

This is a generic feature of circular gravitational wave binaries: the gravitational wave frequency in a circular binary is twice the orbital frequency. In practice what it means is that for each cycle made by the binary motion, the gravitational wave signal goes through two full cycles — there are two maxima and two minima per orbit. For this reason, gravitational waves are called quadrupolar waves

 

Not a guess, not logic. Physics.