Galaxy Structure

Nearby Galaxies and Problems of Structure Formation; a Review

The relativistic hot big bang cosmology predicts gravitational gathering of matter into concentrations that look much like galaxies, but there are problems reconciling the predictions of this cosmology with the properties of the galaxies at modest distances that can be observed in greatest detail. The least crowded place nearby, the Local Void, contains far fewer dwarf galaxies than expected, while there are too many large galaxies in the less crowded parts of our neighborhood. The structures of large galaxies show little relation to their environment, contrary to the standard picture of assembly of galaxies by the gathering of material from the surroundings, and the continued accretion of extragalactic debris has prevented establishment of an acceptable picture of formation of common galaxies with the properties of our Milky Way. There is the possibility that the indirect evidence astronomy affords us has been misinterpreted. But the variety of different challenges makes a strong case that we need a better theory, one that does not disturb the agreement with the network of cosmological tests applied on larger scales and fits what is observed on the scales of galaxies. A promising direction is more rapid structure formation, as happens in theoretical ideas under discussion.