Why Is It Strange to Find Spiral Arms in Spiral

question 38

Multiple Choice

Why is it strange to find spiral arms in spiral galaxies (see Figure 13-24,Comins,Discovering the Essential Universe,6th ed.) ?

• A) Spiral arms require new stars, and previous new stars should have already used up the interstellar medium; no new stars should be forming now.
• B) The variations in speed of the stars across galaxies are not high enough to twist the shape of the arms into a spiral.
• C) There is no known mechanism to generate spiral arms.
• D) The motions of the stars and differential rotation of the galaxy should have wound their arms tightly and made them blend and disappear.

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Definitions:

Return on Total Assets

A financial ratio that measures the effectiveness of a company in generating profit from its overall assets, calculated by dividing net income by total assets.