The best support for the idea that these may not be typical is that an estimate of the Hubble constant based on measurements of gravitational lensing of a distant quasar gives a figure of 37 plusminus 14. (newscientist.com)
Although dark matter does not reflect light — hence the name — astronomers can detect the way its gravity bends the light of distant stars behind it, an effect called gravitational lensing. (scientificamerican.com)
The dark matter distribution was measured by the weak gravitational lensing of the light from visible galaxies by the dark matter (see the relativity chapter). (astronomynotes.com)