Abstract

The past few decades have witnessed the establishment of the ‘standard’ cosmology model, and its remarkable success in explaining cosmic expansion and the large-scale structures in the Universe. However, the nature of dark matter, which is a key building block in the model, remains elusive, but is crucial for understanding cosmic structures at small scales. The first generation of stars, galaxies and black holes formed in small-scale structures at Cosmic Dawn are sensitive to dark matter physics. Therefore, we study the imprints of dark matter physics on early star/structure formation and derive constraints on dark matter model parameters from existing observations. We also discuss the limitations of current observations (in the electromagnetic window) and theoretical models. These limitations motivate us to explore alternative probes of Cosmic Dawn. So we further focus on the gravitational waves from binary black hole mergers as remnants of the first stars. We investigate the properties of binary stars and black holes at Cosmic Dawn and predict the relevant merger rate and mass distribution of binary black holes in mergers, which demonstrates the power of gravitational waves as a unique probe of Cosmic Dawn whose pristine environments produce massive black holes and their mergers efficiently. In general, our work develops theoretical tools to harness future observations of Cosmic Dawn, especially via gravitational waves, as an effective astrophysical laboratory to shed light on the nature of dark matter.