The Interstellar Medium (ISM) is the stuff between the
stars. Most of this stuff consists of gas
and dust . The gas content of the ISM continually decreases
with time as new generations of stars form from the collapse of
giant molecular clouds. The collapse and fragementation of these clouds
give rise to the formation of stellar clusters
. Since the mass function of star formation strongly favors the formation of low mass stars, then each new
star formation locks up available ISM gas into a reservoir of
unevolving low mass stars. Click here
for a schematic representation of the form of the mass function.
The dust particles are sufficiently small that they
short wavelength light more efficiently than long wavelength light.
In fact, blue photons are scattered about 10 times more efficiently
than red photons. Basic Principle of Photon Scattering
No Scattering: Photon Source and