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4.3 Our Galaxy

Our Galaxy probably resembles this model.

Our Galaxy probably resembles this model. lt has a diameter of approximately 100’000 light-years. Note the relatively thin disc. The contour lines represent the space occupied by the 200 billion stars.

On this scale, our solar system would be close to the red mark, at 30’000 light-years from the centre.

The central zone of the galaxy is a region with plenty of old stars, while in the blue areas the stars are more recent. Each star follows a complex trajectory, two examples of which are shown by the red and blue contour lines.

The duration of a typical revolution for a star similar to our Sun, is about 250 million years. lt is by modelling, with the help of powerful computers, that these movements can be demonstrated.

Invisible matter occupies at least three times this diameter. lts exact compo­sition is not known at the present time, but it is the objective of intensive research by astrophysicists.