What is the origin of spiral structure in galaxies?
What is origin of spiral gravitational waves in a spiral galaxy? I read that close to the very core of a spiral galaxy, star density could be so high that stars orbital motions were somehow linked by mutual gravity forces, leading to slow down inner stars and to accelerate outer stars in violation of Kepler’s laws. Is this spiral gravitationnal wave some kind of consequence of this violation ? Thanks for trying to give me some light ! This is a very interesting question and it’s something that extragalactic astronomers have thought about quite a lot. Spiral arms are seen in about two thirds of the brightest 1500 galaxies (as seen from Earth) and we ourselves live in a spiral galaxy, so it must be something very generic that causes it. It turns out that if you assume that the arms are material (i.e. made up of stars that always remain in the arm and are just denser than the stars outside the arm) then very quickly the arms would wind up as the galaxy rotates (well quickly compared to th
