The energy source for infrared-luminous galaxies has long been debated: extreme star formation or growing supermassive black holes? We have been studying infrared galaxies in the millimeter to characterize their emission. One of the intriguing findings is that many infrared galaxies are powered by extremely compact cores, where most of the energy seems to be generated. We have just finished a paper (Aalto+) studying one of the more extreme examples, IC 860. This paper present high-resolution ALMA observations which we interpret as indicating an infrared core size of approximately 10 parsecs with the activity buried behind a column density of 1026 cm − 2. A preprint is available for The hidden heart of the luminous infrared galaxy IC 860 (Aalto+) and the paper has been accepted for publication in Astronomy & Astrophysics.