Dark matter is a mysterious substance that makes up more than 80% of the mass of the universe. It cannot be observed directly because it does not interact with electromagnetic radiation. However, it is possible to see its effect on visible matter such as galaxies and galactic clusters through gravitational interaction.

In recent years, an idea has emerged about how dark matter could help investigate early magnetic fields in the universe. Magnetic fields exist not only around stars and planets, but also extend within galaxies as well as between galaxies. But it’s still not entirely clear how they emerged and why they’ve spread everywhere.

One hypothesis is that weak magnetic fields formed in the early stages of the universe. If this is true, they should leave their mark on the distribution of dark matter, the most abundant form of matter in the universe. Dark matter interacts with normal matter only gravitationally and directly with magnetic fields. But charged particles such as electrons interacting with magnetic fields can gravitationally influence dark matter.

As a result, intergalactic magnetic fields are predicted 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 force exerted by ionized matter along magnetic field lines, dark matter will also accumulate along these lines. Although the gravitational force is very weak, it accumulates over time. Therefore, if magnetic fields existed in the early universe, they should have left traces in the form of dark matter filaments running along these fields.

This effect can lead to the formation of dark matter mini-galaxies around primary magnetic fields. Just as galaxies are surrounded by dark matter halos, these “weak” dark matter halos should be around magnetic fields due to the gravitational interaction of ionized matter. However, charged particles will eventually interact with magnetic fields and most likely neutralize them.

No trace of these early magnetic fields remains in ordinary matter today. However, dark matter microgalaxies may still exist and remain strong sources of gravitational lensing of distant light sources, making their detection possible.

This idea remains purely theoretical. Current telescopes are not yet sensitive enough to measure the gravitational lensing of microgalaxies, so it is not yet possible to test this hypothesis directly. Still, the idea opens new perspectives in the study of early magnetic fields and shows how dark matter can store information about the universe’s past, even things that have long disappeared from our view.