Artist’s impression of a hydroxyl maser. Inside a galaxy merger are hydroxyl molecules, composed of one atom of hydrogen and one atom of oxygen. When one molecule absorbs a photon at 18 cm wavelength, it emits two photons of the same wavelength. When molecular gas is very dense, typically when two galaxies merge, this emission gets very bright and can be detected by radio telescopes such as the MeerKAT. © IDIA/LADUMA using data from NASA/StSci/SKAO/MolView (Link for more information)