HST-Photo: Galaxy NGC5194
Spiral-Galaxy with 2 arms and a closed elliptic ring of Dark-Clouds-Material in the central area of the Galaxy. You also find the Dark-Clouds-Material in the middle of the Galaxyarms. The turnaround-speed of the material in the central Accelerationring was unknown at June 21, 2001.
Theory of determination of development-periods: First, you have to find out the length of an arm of a Spiral-Galaxy. To find out the eject-speed of the Dark-Material-Stream, in this matter you have to explore an active Galaxy, for example, the Galaxy NGC6872 or the Galaxy NGC1365. If you divide the determined length through the stream-speed, then you get an estimate value, how much time it takes to generate the Galaxy-Arms. Thereby you get a part of the complete age of a Spiral-Galaxy. The same method you can use for the following calculation: "How many time ago for the generation of a branch of a Galaxy-Arm and how long needs this period?" If you investigate the above represented Galaxy NGC5194, you see a branch at the outer side of the Galaxy-Arm above the Acceleratorring.