1. As far as I remember, the answer should be: Elliptical galaxies have no spiral arms. Elliptical galaxy has a shape of ellipsoid, every massive elliptical galaxy contains a supermassive black hole at the center. And unlike the spiral galaxy, it has no spiral arms.
2. If my memory serves me well, Hubble’s law is used to determine distances between galaxies. Hubble’s law describes how far the galaxies move away from each other and from the Earth. It means that Universe is expanding.
3. I am completely sure that top-down theory suggests that galaxies formed when massive protogalactic clouds fragmented into smaller gas clouds that then formed into individual galaxies.
4. I think that correct answer looks like this: Astronomers’ everexpanding knowledge of the universe has coincided with the development of the cosmic distance scale, a collection of indirect distance measurement techniques.
5. I am definitely sure that barred spiral galaxies are characterized by a long stretch of stars that extends out beyond the galactic disk. Barred spiral galaxies have big spiral arms which are formed because of the strong compression wave which triggers star formation on the edge of the spiral arms.
6. In my opinion the answer is: The recessional motions of the galaxies prove that the cosmos is not steady and unchanging. It leads us to Hubble’s law that I’ve mentioned before. It proves that galaxies are always in motion.
7. Astronomers are able to measure changes in the rate of universe expansion by observing distant supernovae. In a simple words, supernova is a big explosion of a massive star. After that new bright star appears.
8. According to its definition, protogalactic clouds that have large amounts of angular momentum may develop into spiral galaxies. There are a huge concentration of the stars and gas clouds in the spiral arm. So it’s logical that protogalactic clouds can develop in to spiral galaxies because of certain conditions.
9. According to what I have mentioned before about Hubble’s law, the answer should be: The galaxy clusters distances are expanding. Universe is constantly expanding because of the galaxies’ movement.
10. The Milky Way is an example of spiral galaxies. Our galaxy has several spiral arms and we can see that there are the stars and the gas clouds concentrated in these arms. It’s the main characteristic of spiral galaxy.