J. Anthony Tyson

I am exploring cosmic dark matter observationally. The nature of this transparent dark matter, which dominates the mass budget of the universe, is unknown. Over time, gravity causes the dark matter to clump. In the 1980s, when we applied charge-coupled devices to optical astronomy, my colleagues and I discovered a sky crowded with distant, faint blue galaxies. These faint galaxies may be used as a tool to tomographically reconstruct images of concentrations of intervening dark matter. Einstein showed that mass warps space-time, causing light to travel along curved paths. This in turn results in an imperfect gravitational "lens." Dark matter is revealed by the way it gravitationally warps the images of the background galaxies: a cosmic mirage. To test theories of dark matter, we have been using this technique of gravitational tomography to make direct images of cosmic dark matter on a variety of length scales, ranging from several thousand light-years to tens of millions of light-years.