All the light we cannot see

Observations of the largest scales tell us that about 25% of the energy density in our Universe is in the form of a mysterious component named dark matter. Theoretical explanations of the dark matter phenomenon include primordial black holes, a modification of the laws of gravity or the presence of a new fundamental particle. The latter, particle dark matter, is the only scenario that can explain all observations while not being severely constrained by contemporary measurements. Despite its name, dark matter might produce light through annihilation or decay if it consists of new particles. However, this light is expected to be dim and obscured by astrophysical backgrounds. Nevertheless, one way of searching for dark matter is to hunt for this light by looking at regions in the Universe that contain a high dark matter density. This strategy is known as dark matter indirect detection. In this thesis, we first discuss environmental effects on the light yield of annihilating dark matter and also make a forecast for the sensitivity of a future gamma-ray satellite to detect dark matter. In the second part of the thesis, a contemporary anomaly in dark-matter indirect detection is studied. An anomalous gamma-ray signal, consistent with the expectations of a dark matter signal, is coming from our Galactic Center, a place with one of the highest dark matter densities. We attempt to unveil the origin of this signal, which could come from either dark matter annihilation or an astrophysical source such as millisecond pulsars