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Pulsar Astronomy: Newsletter Challenge (August 2016)

Posted August 01, 2016 12:00 AM
Pathfinder Tags: challenge questions

This month's Challenge Question: Specs & Techs from IEEE GlobalSpec Engineering360:

A double pulsar system is considered a terrific object for studying relativity. However it also can offer great insights into QED. What is it about that particular type of system, particularly the space close to that system, which makes it so useful for studying QED?

And the answer is:

In QED, a large magnetic field can cause the refractive index of space to vary with the polarization of light passing through it, effectively making the light birefringent. Light passing through such space will emerge with a slight elliptical polarization. The amount of elliptical polarization can be used to test QED theories about vacuum polarization.

http://physicsworld.com/cws/article/news/2006/mar/27/optical-rotation-sheds-light-on-vacuum

http://iopscience.iop.org/article/10.1088/0264-9381/26/7/073001

http://arxiv.org/pdf/quant-ph/0504039.pdf

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#1

Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/01/2016 7:07 AM

I'm going to take a stab at this without doing any googling first...

QED (quantum electro-dynamics) is the section of quantum mechanics that studies electrons and mesons; as distinguished from QCD (quantum chromo-dynamics) which studies atomic nucleii and quarks.

Pulsars are believed to be neutron stars, which exist due to electron degeneracy, and which have powerful magnetic fields. Having two neutron stars orbiting each other allows the study of electrons and mesons not only in a pair of powerful magnetic fields, but also orbiting each other with atomic-clock-like precision which allows detailed studies of the pulsars over time. We simply don't see electrons and mesons in such a situation here on Earth. Nearly 100 percent of the information we have about other objects in the universe is due to the study of the photons they emit, and since the photon/boson is the exchange particle for electrons and mesons, we are seeing QED in action under extreme conditions.

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#3
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Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/02/2016 12:47 AM

First, Thank you for doing what the original challenge should have done: defining the acronym. I suspected the question didn't deal with Queen Elizabeth's fourth ship (the "D")...

Now something I hadn't thought about previously: if all the electrons and protons are combined into neutrons, what causes the magnetic field of a neutron star?

BTW, I haven't the slightest idea of an answer to the challenge... I'm a physicist, but definitely a classical one.

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#4
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Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/02/2016 3:16 AM

We'll need to churn through a lot of Queens Elizabeth to get to QED !!

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#5
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Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/02/2016 5:15 AM

A neutron star is not all neutrons...

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#7
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Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/02/2016 10:41 AM

Thanks! I'd never seen such a diagram. Now that I've seen it, and studied it a bit, I'm still not quite sure what I've seen!

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Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/02/2016 4:31 PM

I find it interesting to ponder the structure that holds this object a hair's breadth away from fundamental space/time collapse into a black hole....an invisible framework that supports the structure of the world we live in....a force that separates the dimensions and defines reality...

https://en.wikipedia.org/wiki/Observable_universe#Large-scale_structure

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#6
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Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/02/2016 7:24 AM

That answer to that is not entirely known.

But - our Sun has a magnetic field, and so presumably do all stars. When the neutron star was a 'normal' main sequence star it would have had magnetic field. When that star eventually came to the end of it's life, 'burning' through its nuclear fuel of hydrogen, then helium and other elements, the magnetic field, i.e., the magnetic flux, would likely have become more and more concentrated. Since a neutron star is tiny compared to the original size of the star (maybe 11 Km in diameter, as compared to its original size of, say, 10 million Km), the magnetic field strength would have become billions of times stronger.

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#2

Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/01/2016 2:30 PM

The high gravitation and rapid orbit of the two bodies demonstrates the doppler effect on the timing of the pulsing energy waves showing the combination of photons and electrons in a relativistic manner....This provides the basis for the first theory where full agreement between quantum mechanics and special relativity is achieved.....

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Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/05/2016 5:22 PM

"Scientists discover light could exist in a previously unknown form

http://phys.org/news/2016-08-scientists-previously-unknown.html

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#12
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Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/13/2016 11:14 AM

light is an electromagnetic wave - nothing else?

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#9

Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/03/2016 1:12 PM

QED = Quanten Electro Dynamic?

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#11

Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/08/2016 7:03 AM

My first thought was that some of the (not-analytically-solvable) mathematics might be similar (which they are), but the challenge clarifies that we are looking at effects in the space close to the system.

I can't see that a generalised double-pulsar would necessarily provide resolvable QED effects that a single pulsar would not (though any fast-enough two-spinning-body system would be great for multi-graviton effects - wrong question). But I think interesting observations might be possible when we have two pulsars of very different sizes.
If one pulsar has a very high rotation rate (due to collapse and conservation of angular momentum rather than "concentration" BTW) it would generate enormous magnetic fields in the region near the faster pulsar. From here on I'm even further out of my depth, so it's pure armwaving (please sent the lifeguard).

The very high field could be sufficient to cause photon-electron interaction, whose effects would be clarified if the generated particles then passed close to the slower-rotating pulsar. This too is likely the wrong end of the stick, as this would normally be called Quantum Chromo-Dynamics (and I've no idea how this might be observable in practice).

In terms of exotic QED effects, I think we are left with electron-positron pair interactions. I'm sure that these must be prevalent in the high magnetic field near the smaller, rapidly-rotating pulsar.
But how any such effects might be observable... so moving deeper into the realms of fantasy: the smaller pulsar will presumably not have much atmosphere. Does it move through a concentrated region of the larger pulsar's atmosphere and generate peaks of activity that allow the modest output to be resolved ? Does the field of the larger pulsar periodically focus the radiation? Unfortunately I can't take even this 1%-baked speculation any further...

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#13

Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

08/23/2016 8:27 PM

To the OP

I wasn't aware the fields were high enough for this. Similarly, the accessible literature you link is quite confusing, as relatively short wavelengths are required to avoid the birefringence of hydrogen plasma obscuring the vacuum effect, and the polarisation purity of pulsars deteriorates with reducing wavelength as does the time dependence (randomness). This would appear to make for a horrendously difficult task. Do you have any references that clarify how this sort of aspect is being approached?

Thanks

Fyz

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#14

Re: Pulsar Astronomy: Newsletter Challenge (August 2016)

01/09/2017 6:13 PM

"... a large magnetic field can cause the refractive index of space to vary with the polarization of light passing through it, effectively making the light birefringent."

Close, but it's not the light that is birefringent, it is the anisotropic space near the magnetar that is birefringent, and this birefringence alters the light's polarisation. Birefringence is not a property of light itself, but of the medium through which the light is travelling.

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