The interstar media includes the rarefied substance (gas and dust) electromagnetic radiation, the space beams, neutrino and other kinds of materia which fill the space (see the circulation of gas and dust in the Universe). The interstar media density is 10^-24 - 10^-26 g/sm^3.

The gas-dust nebulas.

The gas-dust nebulas are the inside galaxy clouds of rarefied gas and dust. They may be (containing gas) spheroidal, planetarial, diffusial nebulas. The gas nebulas galaxical are shining due to the transformation of the shot waved (ultraviolet) radiation of the very hot stars located in the nebula or near it into the visible light. The dust nebulas are divided into the light (they are shining by the reflected light) and dark (they may be seen on The Milky Way phone).