based on what you learned about families of galaxies, select all of the correct statements from the following list.
1. The nature of galaxies was not always understood.
2. The nuclei of spiral galaxies appear blue, due to the hot, massive stars.
3. There is no star formation in irregular galaxies.
4. Spiral galaxies do not have much dust in their disks.
5. The halos of spiral galaxies appear reddish, and contain little star formation.
6. There are three basic types of galaxies.
7. Elliptical galaxies do not make new stars.