ASTR 1102 Lecture : Lecture18
Document Summary
We have so far only discussed the how . The galaxy"s spiral arms are one way to compress gas. Giant molecular clouds are concentrated along arms. Spiral arm is like a density wave, compressing gas, triggering star formation. Orion and horsehead nebulae are just the tip of a large iceberg. The whole of orion is covered by giant molecular clouds. Can be seen with microwave emission from carbon monoxide (co) molecules. One cloud will spawn many star clusters. Eject most of the envelope of star at 1000"s of km/s. This expands outwards and collides with the interstellar medium. We think the sun may have formed in this way. 30pc long shockwave (white line) from supernova now forming stars. Also hydrogen to helium, but uses carbon, nitrogen, and oxygen as catalyst. Takes over as stellar cores get hotter than in the sun (e. g. sirius) Takes over when core hydrogen is exhausted. We call he nuclei alpha particles (discovered as radioactivity)
