Unraveling the Mystery of Missing Gamma Rays and Cosmic Magnetic Fields

In their quest to better understand the universe, a team of scientists has published their study results shedding light on a major mystery involving missing gamma rays and vast, invisible magnetic fields in the cosmos. The findings, published in the journal PNAS on November 3rd, offer new insights into these enigmatic cosmic phenomena.

Blazars and the Missing Gamma Rays

Blazars are a type of active galaxy that rely on supermassive black holes and emit narrow jets of particles and radiation at speeds approaching the speed of light. These jets produce high-energy gamma rays reaching several tera-electron volts, which can be observed by ground-based observatories. As these rays travel through intergalactic space, they interact with faint starlight, resulting in the production of electron-positron pairs.

Scientists expect these pairs to collide with cosmic microwave background radiation, generating lower-energy gamma rays. However, space telescopes like NASA’s Fermi satellite have not detected this expected signal, prompting questions about the cause of this discrepancy.

Possible Explanations for the Problem

Scientists have proposed several explanations for this phenomenon. One theory suggests that weak intergalactic magnetic fields deflect the electron-positron pairs, redirecting the resulting gamma rays away from Earth. Another theory, based on plasma physics, proposes that the pairs become unstable as they pass through the thin gas filling intergalactic space, creating magnetic fields and disturbances that drain energy from the stream.

Recreating Cosmic Conditions in the Laboratory

To test these ideas, a research team from the University of Oxford and the UK Central Laser Facility collaborated to use the HiRadMat setup at CERN. They generated streams of electron-positron pairs and used plasma to simulate how blazar jets travel through intergalactic matter.

By measuring the shape of the stream and the magnetic fields it created, the researchers were able to determine whether plasma instabilities were strong enough to disrupt the flow of the stream.

Surprising Results Indicate Ancient Magnetic Fields

The results were unexpected. Instead of the pair stream breaking apart, it remained highly concentrated and nearly parallel, showing little turbulence or magnetic activity. When applied to cosmic scales, this suggests that plasma instability alone is not strong enough to explain the missing gamma rays.

These findings support an alternative explanation that the intergalactic medium contains a residual magnetic field from the early universe. This discovery raises new questions about how these magnetic fields were formed.

Conclusion

This study represents an important step towards a better understanding of complex cosmic phenomena. Through collaboration between different research laboratories and innovative experiments, scientists are able to test theories related to the high-energy universe. Although the results suggest the existence of ancient magnetic fields, many questions remain unanswered. Future observatories are expected to provide more precise data to explore these theories further.