The Astrophysical Journal · 1986 · 90 citations · 0 references
The possibility that galactic halos are composed of baryonic matter is discussed in detail. Specifically, halos composed of snowballs, dust and rocks, planets, stars, dead stellar remnants, and hot and cold gas are considered. The serious problems that would arise for each of these types of matter lead to the conclusion that halos cannot plausibly contain substantial amounts of such matter. This conclusion is considered in relation to big bang nucleosynthesis. Various nonbaryonic candidates for halos are also discussed.