Leading Edge / Winter 2004
Shedding Light on Dark Matter

Scientists find that galaxies are surrounded by huge halos of dark matter


Scientists have made the first-ever measurements of the size and shape of the massive, invisible halos that surround the galaxies. These halos – made of dark matter, named because it emits no light – are more than 50 times more massive than the regions filled with visible stars. Astronomers believe that dark matter and dark energy account for at least 95 per cent of the universe’s contents, making the majority of the universe detectable only indirectly, through its effect on light rays, stars and other gases.

Researchers used weak gravitational lensing, a technique that measures dark matter by the way it distorts light from galaxies, and determined that galaxies are surrounded by huge, slightly flattened halos of dark matter. The halo around the Milky Way galaxy was found to weigh approximately 880 billion times more than our sun, says principal investigator Henk Hoekstra of U of T’s Canadian Institute for Theoretical Astrophysics. This finding supports the “cold dark matter” theory of the universe.


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