Figure 23-34:
Isolated Dark Matter in a Cluster of Galaxies (a) This visible-light image of the Bullet Cluster shows more than a thousand galaxies. The superimposed image in red shows the distribution of the cluster’s hot, X-ray emitting gas, and the blue image shows the distribution of dark matter as determined by gravitational lensing of numerous background galaxies (see Figure 23-30). (b) We can understand the separation of dark matter and gas in this cluster if we assume that dark matter does not feel any force of fluid resistance. This is what we would expect if dark matter responds to gravitational forces only.
Isolated Dark Matter in a Cluster of Galaxies (a) This visible-light image of the Bullet Cluster shows more than a thousand galaxies. The superimposed image in red shows the distribution of the cluster’s hot, X-ray emitting gas, and the blue image shows the distribution of dark matter as determined by gravitational lensing of numerous background galaxies (see Figure 23-30). (b) We can understand the separation of dark matter and gas in this cluster if we assume that dark matter does not feel any force of fluid resistance. This is what we would expect if dark matter responds to gravitational forces only.
(a: NASA/STScI; Magellan/U. Arizona/D. Clew et al.; b: NASA/CXC/M. Weiss.)