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Below is a real photograph of the galaxy, NGC 891. It is seen
almost EXACTLY edge on. It looks suspiciously like the images of
our disk in the previous lecture.
The Disk is extremely flat. Most stars and ALL the gas and dust is found here. 15% of our Galaxy's mass is in the gas and dust (the interstellar medium). The very central portion of the light is blocked out due to that dust. Looking just up or down from the thin disk, we start to see star light. The stellar distribution is slightly fatter than the gas and dust distribution.
In order to see the Nuclear Bulge of our galaxy, it is best to look at infrared wavelengths. The light in the picture below is due entirely to cool stars. They represent a very old population of stars. Many of these stars are in a flattened, spherical orbit around the very center of the galaxy (the nuclear bulge). Cool stars are also detected along the plane of our galaxy, in the disk.
