Answer:
3. Spiral galaxies revolve around a single point and gas spinning arms of stars extending from the center
4. Star 4 will stay on the main sequence for the longest time.
Step-by-step explanation:
A galaxy is a system of gases, dust, and billions of stars and their solar systems, and dark matter which are bound together by gravity. Types of galaxies based on structure are elliptical, spiral, irregular and barred spiral.
Spiral galaxies have a spiral shape consisting of a central bulge, a halo, a disk, and spiral arms. At the center of revolution of the galaxy is the bulge which contains older stars. The disk contains gas, dust and younger stars which extend as spiral arms. The halo is found around the bulge and contains old cluster of stars. Ab example of a spiral galaxy is our Milky Way galaxy.
4. The mass of a star is related to its luminosity as well as its position on the main sequence. High solar mass stars have high luminosity and therefore spend the least time on the main sequence whereas low solar mass stars have low luminosity and spend the most time on the main sequence.
Therefore, Star 4 having the lowest solar mass will spend the most time on the main sequence.