Topics in Our Dynamic Universe.
Some of the Scientists who probed the 13.8 billion year old Universe.
Dark Matter Reveals itself!
The graph shows the rotational speed of stars at different distances from the centre of the galaxy. It is expected that most of the mass of the galaxy is concentrated at its centre, so the further stars are away from the centre the less speed they should have. Think of water swirling down a drain. The water's speed gets faster the nearer it is to the drain.
The graph indicates that the star speeds don't become less the further away from the centre.
This can only be explained by some unseen matter which does not interact with light... hence dark matter.