Molecules in Astrophysics

Abstract

The total mass of our Galaxy is 2 × 1011 M⊙. In the Galaxy more than 90 % of this mass is in the form of stars, and less than 10% represents the tenuous gaseous material located between the stars: the interstellar matter (ISM). The principal constituents of interstellar matter are gas and fine dust particles. The qas consists mainly of hydrogen and helium, with an approximate ratio by mass of H: He: (all heavier elements) = 70:28:2. Dust accounts for about 1 % of the mass of the ISM. The raw material for the formation of young stars is supplied by the ISM. Conversely, stars can reach their final stable “white dwarf” stage only when their mass has decreased to less than 1.4 M⊙. During phases of extensive mass loss, through stellar winds, novae, super novae and planetary nebulae, stars expell mass into interstellar space. Thus, the ISM consists not only of matter left over from the formation of stars but also of matter that was processed through the interior of stars. Obviously stars and the ISM are not two separate entities but are very closely coupled through the cosmic recycling process of star formation and subsequent evolution.