Scott Tremaine, Richard Black Professor, School of Natural Sciences, The Institute for Advanced Study
Few, if any, of the predictions of the standard cold dark matter (CDM) cosmological model have been successful on galaxy-sized or smaller scales. This "small-scale structure problem" is usually explained by the difficulty of modeling baryonic physics (star formation, supernova and black-hole feedback, etc.), but could also reflect shortcomings in our understanding of the nature of dark matter. One intriguing alternative to CDM, often called fuzzy dark matter (FDM), is that the dark matter is an extremely light boson having a de Broglie wavelength comparable to the size of small galaxies. I will describe some of the astrophysical phenomena associated with FDM and how they relate to the small-scale structure problem. These phenomena include a lower limit to the mass of dark halos, the presence of dense Bose-Einstein condensates in the centers of massive halos, evaporation of small halos by tunneling, relaxation due to interference patterns in dark-matter halos, and growth of supermassive black holes by swallowing dark matter.