Light from nowhere

Interaction of particles with the quantum vacuum might explain puzzling gamma radiation

Even in the vacuum of space, light could be slowed down - emitting a telltale radiation, as physicists now posit. © NASA / JPL-Caltech / Gemini / CARMA
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"Impossible" effect: nothing can be faster in the vacuum than the light - actually. But a peculiarity of quantum theory could allow this, as physicists have determined. Even in the vacuum of space, this would give rise to Cherenkov radiation - a wave of photons overtaken by fast particles. This vacuum light could explain where the enigmatic excess of gamma radiation in the heart of the Milky Way and other galaxies is coming from.

The vacuum of the universe is regarded as the epitome of emptiness - quasi as the ground state of the cosmos. Therefore, nothing can move faster in the vacuum than the light, as Einstein recognized. But if you can believe in quantum theory, the vacuum is not empty. After all, quantum fluctuations lead to the formation of virtual particles in the vacuum. These pairs of particles and antiparticles emerge, only to erase a split second later.

Cherenkov light in a nuclear reactor. © Pieck Dario / CC-by-sa 3.0

"Supersonic cone" of light

That's exactly where Alexander Macleod and his colleagues from the University of Strathclyde in Glasgow start. According to their calculations, the quantum fluctuations of the vacuum also produce a measurable effect - the so-called Cherenkov light. This high-energy radiation usually occurs when a medium slows down the light and allows charged particles to fly faster than the light.

One can observe this light effect, for example, in the water-filled reactor vessel of nuclear power plants: electrons rush through the water there so quickly that the light emitted by excited atoms does not lag behind. It forms a type of keel wave quasi a supersonic cone of light. Even with the entry of cosmic particles into the earth's atmosphere or the tanks of detectors, this form of radiation is released.

Magnetic fields as a light brake

However, the deciding factor is that the Chernkov radiation can only be generated in media that slow down the light - and, as is commonly believed, this is not the case with the vacuum. But as Macleod and his team now prove by a physical model, there are exceptions. Because if the virtual particles of the quantum fluctuations are exposed to a strong magnetic field, they too can slow down light. display

"This implies that high-energy particles in space can also release Cherenkov radiation when they fly through strong electromagnetic fields, " the researchers explain. In their calculations, they determined how fast a proton would have to be and which field strengths it needed to fly, so that in a vacuum Cherenkov's light would be released in the form of gamma radiation.

Observable in the environment of pulsars

The result: In the environment of the so-called millisecond pulsars fast-rotating neutron stars with a strong magnetic field the conditions for this "light from nothing" should be given. "For protons of the highest-energy cosmic radiation, the high-energy radiation is completely dominated by the Tscherenkow process, " the physicists explain. In fact, astronomers have already discovered some millisecond pulsars that are only betrayed by gamma radiation - some of which could consist of Cherenkov light.

"Astrophysics thus provides us with environments in which the vacuum Cherenkov effect could be observed, " say Macleod and his team. "Because there we have the presence of very high-energy cosmic rays and strong magnetic fields." A targeted search for gamma rays, which was generated by this process, could prove their theory. Even with the help of very strong lasers, this light could be generated from the vacuum - but so far the technical possibilities are not sufficient, as the researchers discovered.

Explanation for the mysterious Gammagl hen?

The exciting thing about it is that the Vacuum-Cherenkov effect not only explains how high-energy radiation can be released from the apparent void of the vacuum. It could also provide an explanation of where the rambling gamma-ray originated in the heart of many galaxies and the Milky Way galaxy. Until now, astronomers have not been able to discuss a clear explanation for this excess of gamma radiation - both pulsars and dark matter.

"Our theoretical prediction is very exciting, as it could provide answers to some basic questions - including the origin of gamma-raying in the heart of galaxies, " says Macleod's colleague Dino Jaroszynski. "At the same time, it offers a new way to push and test fundamental theories." (Physical Review Letters, 2019; doi: 10.1103 / PhysRevLett.122.161601)

Source: University of Strathclyde

- Nadja Podbregar