Interacting galaxies. Optical image of the system known as NGC 6240. NGC 6240 is probably the result of the merging of two spiral galaxies and this causes its peculiar shape. The two bright and compact sources seen at centre are thought to be the nuclei of the two interacting galaxies. NGC 6240 is also one of the strongest MASER (Microwave Amplification by Stimulated Emission of Radiation) emitters. In MASER emission some molecules such as the OH radical and the water molecule H2O, absorb energy either from collisions with other molecules or from stellar radiation and convert this energy into strong emission lines at radio wavelengths.