by Boris SHUSTOV, RAS Corresponding Member, Director of the Institute of Astronomy, Moscow
The hidden mass idea implies that we live in the Universe where unobservable matter dominates. The nature of this matter is obscure and may be quite unusual. But the hidden mass is perceived by most astronomers as a quaint but a plainly established thing. Since different and not always consistent definitions of this unobservable component of the Universe occur even in the literature, I shall use what appear to me as the most cogent definitions.
The hidden mass (HM) is matter which exists in the Universe but is unobservable. It consists of two different components: (1) Dark matter (DM) of the unknown nature whose existence is manifest only implicitly through gravitational action on different objects of the Universe and (2) baryonic dark matter (BDM) which is just common matter, unobservable though due to our limited possibilities.
Physicists and astronomers discuss a wide range of possibilities in explaining the physical nature of hidden mass carriers--from hypothetic elementary particles down to dwarf stars and black holes. The masses of candidate carriers differ by more than 70 orders of magnitude.
The main question about dark matter is quite straightforward: What is it? So far there is no generally accepted and cogent answer despite the eighty-year history of research. Only one thing is obvious: DM exceeds BDM greatly.
Baryonic matter is just common substance which forms us and the world we live in. The nature of baryonic matter and many of its characteristics are studied mostly (with respect to astronomical objects anyway), by observation methods. We observe such matter in the
Fig. 1. Microphotometer curve, i.e. radial brightness distribution (upper panel) and the galaxy rotation curve NGC~3198 obtained by observations of neutral hydrogen at 21 cm (lower panel). The rotation curve is resolved into three compon ... Читать далее