Molecules have a rich spectrum of radio-frequency line emission, and many species have been detected in the ISM, ranging from carbon monoxide to water to formaldehyde to alcohol. The gas is clumped into clouds of various sizes, some truly enormous. Think of the difference between looking at a clear blue sky and a cloudy one. Interplanetary dust also reddens starlight, and causes it to become polarized. The energy it radiates is provided by a continued slow shrinkage, converting gravitational energy into heat to replace the energy which the protostar is radiating away.
More massive stars go through each stage far more rapidly than less massive ones.
Copyright 2000 by James N. Douglas. All rights reserved.