Structure of the Galaxy.
Reading: Kaufmann, Chapter 25, Our Galaxy.
The evidence we have seen suggests that we are inside one of these. [This
is the spiral galaxy M83 in blue light].
Here is a schematic picture of the parts of a spiral galaxy. Seen
edge on.
Here is the same picture with names for the parts.
- We have seen the disk stars in visible and near infrared pictures.
- We have seen the 21 cm radiation from hydrogen gas in the disk.
- We have seen the far infrared radiation from dust in the disk.
- Some stars are halo stars. (From position and motion.)
- Here is a globular cluster (M3). Here is M5.
Motion in the Galaxy
Before going any further, it is important to understand that all of
this is in motion. We first study motion
and gravity.
Application to the Galaxy.
- The stars and other matter that make up the Galaxy would just move off
into space if it weren't for the gravitational force created by all
the mass in the Galaxy.
- The objects in the disk of the galaxy have orbits in the plane
of the disk.
- How do we know this?
- If the orbits weren't in the plane of the disk, the disk couldn't
stay a disk.
- We can look at motions using Doppler shift measurements.
- The objects in the halo have random orbits.
- How do we know this?
- We can look at motions using Doppler shift measurements.
Davison E. Soper, Institute of Theoretical Science,
University of Oregon, Eugene OR 97403 USA
soper@bovine.uoregon.edu
