Vince 49

In the last few years it has become possible to create images of dark matter using weak gravitational lensing. The image at the first link below was on the cover of Nature some years ago. The lensing theory, including cosmic shear, is rather complicated. You can find a reasonably detailed explanation on Wikipedia--see the second link. Below is a rather simplified version of how it works. You build up the image in slices. All the galaxies at a given Z (red shift) are the same distance from Earth, corresponding to one slice. The average elliptical eccentricity of tens of thousands of these galaxies will be very close to zero. However, if there is a significant gravitational field, the galaxies will appear to be slightly elongated in the direction of the gravitational force, providing some information about the magnitude and direction of what ever is creating the gravitational field. Repeat this for a range of Zs, and you can build up a three-dimensional image, such as that shown in the attachment below. These results provide rather convincing evidence that there is something massive out there, that is invisible in the electromagnetic spectrum. Link to 3D image of dark matter: https://goo.gl/images/hBq2H3 Link to Wikipedia entry on weak gravitational lensing: https://en.wikipedia.org/wiki/Weak_gravitational_lensing