We present the results of a multi-wavelength investigation of the very X-ray luminous galaxy cluster MACSJ0553.4 - 3342 ( z { = } 0.4270 ; hereafter MACSJ0553 ) .
Combining high-resolution data obtained with the Hubble Space Telescope and the Chandra X-ray Observatory with groundbased galaxy spectroscopy , our analysis establishes the system unambiguously as a binary , post-collision merger of massive clusters .
Key characteristics include perfect alignment of luminous and dark matter for one component , a separation of almost 650 kpc ( in projection ) between the dark-matter peak of the other subcluster and the second X-ray peak , extremely hot gas ( k T { > } 15 keV ) at either end of the merger axis , a potential cold front in the East , an unusually low gas mass fraction of approximately 0.075 for the western component , a velocity dispersion of 1490 _ { -130 } ^ { +104 } km s ^ { -1 } , and no indication of significant substructure along the line of sight .

We propose that the MACSJ0553 merger proceeds not in the plane of the sky , but at a large inclination angle , is observed very close to turnaround , and that the eastern X-ray peak is the cool core of the slightly less massive western component that was fully stripped and captured by the eastern subcluster during the collision .
If correct , this hypothesis would make MACSJ0553 a superb target for a competitive study of ram-pressure stripping and the collisional behavior of luminous and dark matter during cluster formation .