The standard model of cosmology states that the dark matter present in the Universe consists of particles that mainly interact gravitationally. This model is extremely successful in explaining the large scale structure: from the Cosmic Microwave Background to how galaxies distribute in the Universe.
In this scenario, the dark matter dominated formation of structure is hierarchical: small structure form first, and then acts as building blocks to form bigger structure. One of the key predictions of this scenario, or any scenario where formation of structure is hierarchical, is the presence of hundreds to thousands of small dark matter halos orbiting galaxies like the Milky Way. However, due to their dark nature and small scales, these have proven difficult to find. Nevertheless, while most of the smallest of the dark halos will remain dark forever, some will be lit by small and dim galaxies, providing a window of opportunity to probe the nature of dark matter and the formation of structure at the smallest scales.
In this contribution, I will present some results of a new quest for the search of the dark halos around the Milky Way, via the detection of small satellite galaxies. By improving the detection algorithms and by the use of new deep wide surveys, I have pushed the detection limits yielding several new discoveries, including the discovery of the enigmatic galaxy Crater 2. Even when being the fourth largest in the vicinity of the Milky Way, Crater 2 remained hidden until very recently due to its extreme properties. These same properties may be in tension with our current models of the Universe posing interesting new challenges to the standard model of cosmology.