How mysterious dark matter helps solve the mystery of magnetic fields
Dark matter — This is a mysterious substance that makes up more than 80% of the mass of the Universe. It does not interact with electromagnetic radiation, so it cannot be observed directly. However, it is possible to see its influence on visible matter such as galaxies and galaxy clusters through gravitational interactions.
In recent years, an idea has emerged regarding how dark matter could help study early magnetic fields in the Universe. Magnetic fields are present not only around stars and planets, but also extend throughout the galaxy, as well as between galaxies. However, it is still not entirely clear how they arose and why they are spreading everywhere.
One hypothesis is that weak magnetic fields formed in the earliest stages of the Universe. If this is true, then they should leave their traces in the distribution of dark matter, which is the most abundant form of matter in the Universe. Dark matter interacts with ordinary matter only gravitationally and does not interact directly with magnetic fields. However, charged particles such as electrons that interact with magnetic fields can exert a gravitational influence on dark matter.
As a result, intergalactic magnetic fields are expected to accumulate electrons and ionized intergalactic hydrogen along their lines, making these regions slightly denser compared to the rest of intergalactic space. Due to the gravitational influence of ionized matter along magnetic field lines, dark matter will also accumulate along these lines. Even though the gravitational effect is very weak, it accumulates over time. Thus, if magnetic fields really existed in the early Universe, then they should leave traces in the form of dark matter threads extending along these fields.
This effect can lead to the formation of dark matter minigalaxies around primordial magnetic fields. Just as galaxies are surrounded by dark matter halos, these «faint» Dark matter halos should be present around magnetic fields due to the gravitational interaction of ionized matter. However, over time, charged particles will interact with magnetic fields and most likely neutralize them.
At present, there are no traces of these early magnetic fields left in ordinary matter. However, dark matter microgalaxies may still exist and remain influential sources of gravitational lensing of distant light sources, which makes them possible to detect.
This idea remains purely theoretical. Existing telescopes are not yet sensitive enough to measure gravitational lensing of microgalaxies, which means it is not yet possible to directly test this hypothesis. However, this idea opens up new perspectives in the study of early magnetic fields and demonstrates how dark matter can store information about the past of the Universe, even that which has long disappeared from our sight.