F1 - ISM
- the InterStellar Medium (ISM) is the material filling the volume between the stars
- the origin of ISM:
- unprocessed matrials that have never been in stars, originating from nucleosynthesis post the Big Bang
- processed materials from previous stellar generations that were released from supernovae
- materials expelled by massive young stars via stellar winds (radiation pressure)
- it comprises mainly of:
- gas: atoms and molecules at very low density,
cm , as low as cm - dust: everything else, mainly micron-sized silicon and carbon aggregates, similar to the composition of candle soot, that can absorb radiation and subsequently re-radiate it as a black body
- gas: atoms and molecules at very low density,