For example, if a distant galaxy emits light in our direction, it may be diverted slightly in its otherwise straight path. Like a glass lens being placed in front of a lightbulb, the galactic light will distort from our viewpoint - the heavier the mass, the greater the distortion.
This distortion is known as "gravitational lensing" and it can be used as a tool to detect things like galaxies, black holes and, you guessed it, dark matter.
NEWS: The first-ever direct evidence of dark matter was detected in 2006 amid fallout from galactic collisions.
By combining the Hubble observations of gravitational lenses with spectroscopic red shift observations from telescopes on Earth, the 3D location of clumps of mass (dark matter, galaxies, black holes etc.) can be found. In this case, the white, cyan, and green regions are closer to Earth than those indicated in orange and red.
How does red shift work? Get the cosmic details on HowStuffWorks.com.
To produce this scene, astronomers used Hubble to survey over 446 000 galaxies, notching up over 1000 hours of observing time on the space telescope. This is the largest ever survey carried out by Hubble.