Imaging the invisible
Ken Tapping, January 18, 2012
Even today, my favourite science fiction movie is “Forbidden Planet”. This old movie, dating back to the 1950’s, has probably stood the test of time because it is based upon a good solid source, Shakespeare’s play, “The Tempest”.
One of the principal characters in the movie is a monster of almost infinite power, and which also happens to be invisible. We only sense its presence by seeing its footprints appear in the ground or by things being knocked over as it passes by. This evidence is enough to convince us that something is there even though we cannot see it and don’t know what it is. This is also quite similar to how we consider dark matter.
Dark matter is totally invisible; we only know it’s there because of its gravitational tugging at the things we can see, like stars and huge clouds of gas and dust making up galaxies. From the extent of this tugging, we know that there is a lot of this invisible material. There is roughly five times as much dark matter as “ordinary matter” – the stuff we’re made of. It plays a major role in the workings of galaxies and the universe as a whole, and yet we can’t see it. That is, until recently, when a team of astronomers used the Canada France Hawaii Telescope to make detailed maps of the observable effects of the dark matter. They then used these maps to image the things causing them.
One of the predictions made in Einstein’s “Theory of Relativity,” is that light is deflected by gravity, just as it is bent by a prism or focused by a lens. For small things like us, or the Earth for that matter, the effects are tiny; but for large things like galaxies, or huge clumps of dark matter, the effects are easy to detect. This process is used in what has become known as “gravitational lensing”.
The Canada-France-Hawaii Telescope, located at the Mauna Kea Observatory in Hawaii.
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