This shows gas (first) and stars (second) in the merger, then both at the same time in a multi-panel view from two different viewing angles. Gas: color shows gas temperature from 1e4 K (blue) to 1e6 K (red). Stars: color shows mean stellar age, from 1e7 yr (blue) to 1e9 yr (red). Brightness shows projected surface density, scaled logarithmically. Credit: Volker Springel