First signs of weird quantum property of empty space?

November 30, 2016, ESO
This artist’s view shows how the light coming from the surface of a strongly magnetic neutron star (left) becomes linearly polarised as it travels through the vacuum of space close to the star on its way to the observer on Earth (right). The polarisation of the observed light in the extremely strong magnetic field suggests that the empty space around the neutron star is subject to a quantum effect known as vacuum birefringence, a prediction of quantum electrodynamics (QED). This effect was predicted in the 1930s but has not been observed before. The magnetic and electric field directions of the light rays are shown by the red and blue lines. Model simulations by Roberto Taverna (University of Padua, Italy) and Denis Gonzalez Caniulef (UCL/MSSL, UK) show how these align along a preferred direction as the light passes through the region around the neutron star. As they become aligned the light becomes polarised, and this polarisation can be detected by sensitive instruments on Earth. Credit: ESO/L. Calçada

By studying the light emitted from an extraordinarily dense and strongly magnetized neutron star using ESO's Very Large Telescope, astronomers may have found the first observational indications of a strange quantum effect, first predicted in the 1930s. The polarization of the observed light suggests that the empty space around the neutron star is subject to a quantum effect known as vacuum birefringence.

A team led by Roberto Mignani from INAF Milan (Italy) and from the University of Zielona Gora (Poland), used ESO's Very Large Telescope (VLT) at the Paranal Observatory in Chile to observe the neutron star RX J1856.5-3754, about 400 light-years from Earth.

Despite being amongst the closest , its extreme dimness meant the astronomers could only observe the star with visible light using the FORS2 instrument on the VLT, at the limits of current telescope technology.

Neutron stars are the very dense remnant cores of massive stars—at least 10 times more massive than our Sun—that have exploded as supernovae at the ends of their lives. They also have extreme magnetic fields, billions of times stronger than that of the Sun, that permeate their outer surface and surroundings.

These fields are so strong that they even affect the properties of the empty space around the star. Normally a is thought of as completely empty, and light can travel through it without being changed. But in quantum electrodynamics (QED), the quantum theory describing the interaction between photons and charged particles such as electrons, space is full of virtual particles that appear and vanish all the time. Very can modify this space so that it affects the polarisation of light passing through it.

Mignani explains: "According to QED, a highly magnetised vacuum behaves as a prism for the propagation of light, an effect known as vacuum birefringence."

Among the many predictions of QED, however, vacuum birefringence so far lacked a direct experimental demonstration. Attempts to detect it in the laboratory have not yet succeeded in the 80 years since it was predicted in a paper by Werner Heisenberg (of uncertainty principle fame) and Hans Heinrich Euler.

This wide field image shows the sky around the very faint neutron star RX J1856.5-3754 in the southern constellation of Corona Australis. This part of the sky also contains interesting regions of dark and bright nebulosity surrounding the variable star R Coronae Australis (upper left), as well as the globular star cluster NGC 6723. The neutron star itself is too faint to be seen here, but lies very close to the centre of the image. Credit: ESO/Digitized Sky Survey 2
"This effect can be detected only in the presence of enormously strong magnetic fields, such as those around neutron stars. This shows, once more, that neutron stars are invaluable laboratories in which to study the fundamental laws of nature." says Roberto Turolla (University of Padua, Italy).

After careful analysis of the VLT data, Mignani and his team detected linear polarisation—at a significant degree of around 16%—that they say is likely due to the boosting effect of vacuum birefringence occurring in the area of surrounding RX J1856.5-3754.

Vincenzo Testa (INAF, Rome, Italy) comments: "This is the faintest object for which polarisation has ever been measured. It required one of the largest and most efficient telescopes in the world, the VLT, and accurate data analysis techniques to enhance the signal from such a faint star."

"The high linear polarisation that we measured with the VLT can't be easily explained by our models unless the vacuum birefringence effects predicted by QED are included," adds Mignani.

"This VLT study is the very first observational support for predictions of these kinds of QED effects arising in extremely strong magnetic fields," remarks Silvia Zane (UCL/MSSL, UK).

Mignani is excited about further improvements to this area of study that could come about with more advanced telescopes: "Polarisation measurements with the next generation of telescopes, such as ESO's European Extremely Large Telescope, could play a crucial role in testing QED predictions of vacuum birefringence effects around many more neutron stars."

"This measurement, made for the first time now in visible light, also paves the way to similar measurements to be carried out at X-ray wavelengths," adds Kinwah Wu (UCL/MSSL, UK).

This research was presented in the paper entitled "Evidence for vacuum birefringence from the first optical polarimetry measurement of the isolated neutron star RX J1856.5−3754", by R. Mignani et al., to appear in Monthly Notices of the Royal Astronomical Society.

Explore further: Hubble captures the beating heart of the Crab Nebula

More information: Research paper: … eso1641/eso1641a.pdf

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1.3 / 5 (3) Nov 30, 2016
I think the word, "prism," is wrong. All this time, I've been told repeatedly that light cannot be bent by a magnetic field (except as energy equivalency to mass bends spacetime). Light has never been detected as bent when passing through even the most powerful magnetic fields known in the Universe, magnetars.
4.8 / 5 (16) Nov 30, 2016
It's not bent. It's polarized. There's a huge difference between the two.
1.4 / 5 (9) Nov 30, 2016
Mignani explains: "According to QED, a highly magnetised vacuum behaves as a prism for the propagation of light, an effect known as vacuum birefringence."

Perhaps this effect is responsible for what current science calls 'gravity lensing' or 'gravity waves' or even black holes. I understand magnetic waves are 'solitons' and perhaps these are responsible. Linear polarization can only just now be measured and hopefully magnetars births can be discovered.
1 / 5 (7) Nov 30, 2016
In SQK, empty space is not empty. It is full to the brim and extremely dense. It is just that the diffusive ocean of sub quantum elementals are each too small to ever be directly detected. It is their propagating reactive interaction under proper diffusive conditions that we detect as a sub-atomic particle. So matter itself is a form a wave. Some particles pass right through the earth for example, neutrinos. As a wave, that effect is much more easy to logically explain.

And this property can also explain the double-slit experiment, as the diffusive concentration pattern surrounding the propagating particle precedes the particle itself, casting an interference pattern from between the slits until the particle actually passes through one slit or the other.
4 / 5 (12) Nov 30, 2016
Perhaps this effect is responsible for what current science calls 'gravity lensing' or 'gravity waves' or even black holes. I understand magnetic waves are 'solitons' and perhaps these are responsible. Linear polarization can only just now be measured and hopefully magnetars births can be discovered.


Hint: Throwing together a bunch of scientific words in a sentence does not make you look smart. It only makes you look smart if the sentence makes sense (i.e. if it is clear that you know what those words mean - which you very definitely don't).
4.7 / 5 (14) Nov 30, 2016
Birefringence, polarization, is not the same thing as bending. Hence it is not the same thing as lensing. No, magnetic fields aren't 'gravitational lenses.' Magnetic effects don't explain the observations we see that support general relativity. This is a special case where some interesting quantum mechanics occur that causes a very very tiny effect in the presence of exceedingly huge fields.
5 / 5 (4) Nov 30, 2016
Probably Mignani refers to a Nicol Prism, a device that indeed polarises light.

Nov 30, 2016
This comment has been removed by a moderator.
1 / 5 (7) Nov 30, 2016
Still trying to flog the neutron star model, but replace it with a gamma-ray source and there is then an alternative way to produce the electric field needed to create the magnetic field, and it requires no gravity and thus no hypothesised neutron stars.
2.3 / 5 (3) Nov 30, 2016
Its there not so understanding, of the neutron stars magnetic field that the gravity of the star captures more electrons in orbit around the star than can be exchanged with the suface atoms electrons on the star at the speed of light in time, so it has two magnetic fields a surface magnetic field and an orbiting envelop magnetic field held by gravity.
2.3 / 5 (3) Nov 30, 2016
Can anyone explain the dark areas that surround these brightest stars in the photo? Are they some type of photographic artifact?
Nov 30, 2016
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3.7 / 5 (3) Nov 30, 2016
Many thanks, tesschris!

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