3 ms·
the rotation of a galaxy isnt the same thing as the rotation of the stars contained within in. The rotation of the galaxy is measured by the rotation of arms/ot
by throwaway2048 9y ago
the rotation of a galaxy isnt the same thing as the rotation of the stars contained within in. The rotation of the galaxy is measured by the rotation of arms/other features, which are due to a traveling density wave (think about how traffic speeds up/slows down)
- wyager 9y agoIf stars orbit faster than arms, doesn’t this mean that stars have to occasionally change which arm they’re in? How does that work - some sort of gradual re-clumping of stars?
- mkempe 9y agoYes, our solar system travels from arm to arm! while the overall shape of the galaxy remains. By the way, our transit between and into these galaxy arms is theorized to coincide with past mass-extinction events, across tens of millions of years.
- civilian 9y agoWhaaat! I never heard about the galaxy arm transit coinciding with mass extinction events. I'm about to google, but do you have a favored source?
- mkempe 9y agoI commented here 10 months ago https://news.ycombinator.com/item?id=14291004 https://news.ycombinator.com/item?id=14291004 in relation to "Mass Extinction and the Structure of the Milky Way (2013) (arxiv.org)"
- civilian 9y agoBut, the arms don't rotate either! There are some great animations here: https://en.wikipedia.org/wiki/Density_wave_theory https://en.wikipedia.org/wiki/Density_wave_theory The article was about stars on the edge of a galaxy. > “But regardless of whether a galaxy is very big or very small, if you could sit on the extreme edge of its disk as it spins, it would take you about a billion years to go all the way round.”
- dwringer 9y agoAs another commenter points in another thread, this article is explcitly about the red-shift-calculated velocity of stars at the outer edge of galaxies, and not about the spiral arms' apparent motion.