An article published in the journal “Classical and Quantum Gravity” describes the reconstruction of the map of magnetic fields generated after the Big Bang in the “cosmic neighborhood”. A team of researchers used an algorithm called BORG (Bayesian Origin Reconstruction from Galaxies), developed to work on large-scale structures, to data from the 2M++ galaxy catalog to calculate how these magnetic fields should look like today within a radius of 300 million of light years around the Earth.
The primordial magnetic fields produced in the universe after the Big Bang together with elementary particles have today an extremely weak intensity and consequently are impossible to measure directly with the current instruments. However, knowing its distribution would still be useful in research on cosmological events such as inflation, the period in which the early universe had an exponential expansion, and the recombination, the epoch in which electrons and protons started forming hydrogen atoms.
In this research led by the Max Planck Institute for Astrophysics in Germany, these magnetic fields were estimated through the so called Harrison mechanism, which exploits whirling movements in the fluctuations of matter similar to the ones that formed the observed structures. This is a very complex problem and so is the research needed for those magnetic fields’ reconstruction.
To achieve that reconstruction they needed to know the plasma vortices existing right after the Big Bang. Their movements produced electrical currents due to friction, thus generating magnetic fields. The information needed are contained in the distribution of galaxies because it was produced by the motion of matter since the birth of the universe.
The laws that govern galaxy formation are well known and this allowed the researchers to trace the evolution of the distribution of matter around the Earth with good accuracy. That information allowed to reconstruct the magnetic fields generated by the Harrison effect for a radius of about 300 million light years.
The calculations took tens of thousands of hours of a supercomputer, confirming the task’s complexity. The magnetic fields are very weak, with values lower than the the ones that can currently be measured. This is a problem because it means that it’s impossible to verify the correctness of the reconstruction.
The researchers compared their reconstructions to gravitational waves, which at the time when Albert Einstein predicted their existence were impossible to detect. This is a known problem in which theoretical physics precedes the experimental one and we have to hope for technological progress in order to obtain a verification of the predictions.