AST 341 Lecture Notes - Lecture 23: Minimum Mass, Gas Constant, Solar Mass

• School: Stony Brook University
• Department: Astronomy
• Course: AST 341
• Professor: Rosalba Perna

Document Summary

After discussing stars during their life and after their death, we now turn to the issue of star birth. This mixture of gas and dust that permeates the space between stars in a galaxy, is what we refer to as the interstellar medium. In our galaxy, it amounts to a few percent of the total galactic mass, some 109m , concentrated in a very thin disk, less that. 103 lightyears in thickness and 105 lightyears in diameter. Its average density is extremely small, about one particle per cubic centimeter, corresponding to a mass density 10 24 g cm 3. This medium is so rare ed that in an ordinary laboratory on earth it would be considered a perfect vacuum. The predominant component of galactic gas is hydrogen, amounting to about 70% of the mass, either in molecular form (h2), or as a neutral atomic gas (hi), or as ionized gas (hii), depending on the prevailing temperature and density.