Dogs that Don't Bark (The Tale of Baryonic Dark Matter in Galaxies)

11 Jun 2018

Fifteen years or so ago, it was commonly argued; ``If we want to believe the observations rather than our prejudice, we should take as our best bet that dark haloes are baryonic.'' Such a viewpoint is not often heard today. This change-of-mind has been enforced upon us largely by the microlensing experiments. Particle dark matter differs from (most types of) baryonic dark matter in that it does not produce microlensing events. The familiar parade of baryonic candidates has now been whittled down, and perhaps only one remains as a possible substantial contributor to the dark matter in the Galaxy's halo. This review assesses the distribution of missing matter in the Galaxy, the likely baryonic dark matter suspects, the evidence from microlensing and from the halo white dwarf searches.