Even though dark matter makes up about 85% of mass in the universe, its mysterious nature renders it largely unknown. Dark matter is precisely ‘dark’ because it does not interact with light, making it very challenging for astrophysicis to study it. Typically astrophysicicsts rely on light as their primary source of information. Therefore, we still do not know what dark matter consists of, but there are many good guesses as to the kinds of particles it could be. Depending on the mass of these dark matter particles, it will affect how the earliest galaxies form and evolve.
At the time when the universe begins to clump together, forming structures like galaxies and stars, it is dominated by matter and gravitational interactions. Since dark matter comprises the largest portion of material in the universe, its immense mass and quantity define how the universe takes shape. Dark matter acts as the glue that holds together the structures in the universe.
Once the early, young galaxies have formed, the gas will begin to be ionized by the energy from star formation in the new galaxies. This has a strong effect on the 21 cm signal. New radio experiments such as HERA (Hydrogen Epoch of Reionization Array) and SKA (Square Kilometer Array) will map out the 21 cm signal over the next decade and contribute to further investigating how the first galaxies form and what type of dark matter shapes the universe.
Jo Verwohlt 