Comment by antognini
I studied these objects for my first research paper in grad school. (You can see a few images of some of the objects I found in Figure 3 of my paper [1]) In essence the jet blows a hot bubble into the gas that comprises the intracluster medium of the galaxy cluster. Over time synchrotron radiation causes the bubble to cool down and eventually (maybe on the order of a few 100 million to a billion years if I recall right) the bubble comes into thermal equilibrium with the surrounding gas.