The Disk The disk of the Galaxy contains the spiral arms. Astronomers have been attempting to find the details of the structure of spiral arms in the galaxy for some time now. The origin of the spiral structure is still a matter of some debate, but the prevailing explanation right now is something called spiral density waves. Which spiral arm do we live in? There is not general agreement on that point, simply because it is so hard to map the arms. Most researchers would say that the Sun is in the Orion Arm. We speak of two different populations of stars. Population I type stars are found in the disk of the galaxy.