Galaxy star formation
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by
jim2mars
How do we know that star formation has stopped?
Is there something about the spectrum of light from the galaxy that enables us to infer that the rate of star formation is very low or has stopped?Posted
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by
JeanTate
Low-level star-formation is very hard to detect, unless the galaxy is quite close (so it appears large, and maybe we can see individual star clusters or even stars).
As I understand it, most star-formation occurs in 'giant molecular clouds', and results in a few massive (and very bright and blue) stars, more less massive ones (yellow and not so bright, like our Sun), and huge numbers of tiddlers (red, and so faint we can't see any in the night sky, without a telescope). The massive stars 'die young', exploding as supernovae after just a few (tens of) millions of years. Before the remnants of the birth clouds have been dispersed, they glow with highly distinctive colors (basically just a few, narrow, lines, often called nebular lines). The spectroscopic signature of star-forming regions is thus very clear; from the continuum which keeps rising towards the blue, to the strong (and narrow) emission lines.
Posted
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by
astropixie
scientist
hi jim2mars. yes, there are a couple spectral indicators that show whether new stars are forming, or have formed recently. in short, a lack of strong emission lines and an overall spectral shape that looks like A-type stars. for much more detail, you can check this out: http://postquench.blogspot.com/
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