Spiral Arms of Galaxies
Apr. 27th, 2006 08:55 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
snydersLearned today that sprial arms of galaxies do not rotate together with the stars. In fact stars rotate much slower at almost constant velocities (because most of the galaxy mass is due to the dark matter), thus stars close to the center make several turns while far stars do a single turn.
"Like the stars, the spiral arms also rotate around the center, but they do so with constant angular velocity. That means that stars pass in and out of spiral arms. The spiral arms are thought to be areas of high density or density waves. As stars move into an arm, they slow down, thus creating a higher density; this is akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because the high density facilitates star formation and they therefore harbor many bright and young stars." (from wiki)
"Like the stars, the spiral arms also rotate around the center, but they do so with constant angular velocity. That means that stars pass in and out of spiral arms. The spiral arms are thought to be areas of high density or density waves. As stars move into an arm, they slow down, thus creating a higher density; this is akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because the high density facilitates star formation and they therefore harbor many bright and young stars." (from wiki)
