March 31: David Wittman
"Gravitational Lensing and Dark Matter"







Abstract

Roughly 90% of the matter in our universe is dark: We can't see it directly and we don't know what it is. But a technique called gravitational lensing allows us to map out this dark matter because its gravity bends light from background galaxies, distorting their images like a funhouse mirror. This lensing effect is strongest in the densest regions of the universe, where it has spectacular effects such as shown in the picture. To learn something about the universe in general, though, we must extend this technique to more typical regions of the universe, where the effect is much weaker. We have recently discovered that this effect can be detected anywhere on the sky, which leads to a rough estimate of the total amount of dark matter in the universe.