Events at Physics
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belong to the most poorly understood class of astronomical objects
and serve as the most challenging targets of astrophysical researchfor various reasons:
At first, in LCDM cosmology a huge number of subhalos are expected
to surround massive galaxies what is contrasted by the observed number of satellite galaxies around the MWG. In addition, it is debated whether the recently detected ultra-faint dSphs can account for this mismatch.
Secondly, the still at present observable accretion of satellite galaxies by the MWG should have led to the built-up of the Galactic halo and left behind kinematic and chemical witnesses by their stars. Besides that these expected signatures and similarities between halo stars and existing dSphs are not observed, also their spatial distribution and number pose serious questions to our understanding of satellite-galaxy
evolution. To solve these problems numerical simulations from cosmological to galactic scales and semi-analytical galaxy models have been undertaken by numerous authors which will be highlighted, but also critically reviewed here.
New comprehensive approaches will be presented and their results compared with observations.