| spiral density wave | has definition A wave, due to a local increase in the gravitational field, that produces a series of alternate compressions and rarefactions as it propagates with fixed angular velocity in a rotating galaxy. The compression also acts on interstellar gas in the galaxy, which is triggered to form stars on the leading edges of the spiral arms. The large-scale structure of spiral galaxies can be understood in this way. |  |
| is a kind of galaxy theory | |
| galaxy theory | has domain extragalactic astronomy | |
| theory | has validity correct or incorrect with caveats | |
| has author or reasearch group | |
| has date or a range of dates for which the theory was active | |
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