The Dark Matter Mystery: Gravitational Lensing

The Mystery of Dark Matter (3/4): Gravitational Lensing.

A mystery exists! Galaxies do not seem to have enough mass for stars to orbit at their observed speeds. Galaxies should be flying apart, but they don't. Why not? Explore the surreal world of dark matter - one of the universe's greatest mysteries.

This presentation is available to educators on DVD and comes complete with specially-crafted teacher notes.
• http://www.perimeterinstitute.ca

The Mystery of Dark Matter Video Game
• http://perimeterinstitute.ca/dark_mat...

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A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is "bent" around a massive object (such as a cluster of galaxies) between the source object and the observer.

The process is known as gravitational lensing, and is one of the predictions of Albert Einstein's general theory of relativity.

The gravity from a massive object (such as a galaxy cluster or black hole) is warped space-time, bending everything in it—including the paths followed by light rays from a bright background source.

This alters the time taken for the light to reach an observer, and can both magnify and distort the apparent image of the background source.

• http://en.wikipedia.org/wiki/Gravitat...