What is the origin of the cosmic diffuse infrared background ?
A study, based on observations by the ISO infrared satellite, brings today a essential answer to this very important astrophysical question. With the help of deep sky images, obtained at the wavelength of 15 microns (medium infrared), a team of astronomers of the Service d'Astrophysique du CEA, in the context of an international collaboration, have discovered a large number of starburst galaxies which have been overlooked in previous observations at other wavelengths. These galaxies are indeed "shy" because their stellar birth regions are masked by a screen of interstellar dust and therefore only revealed in the infrared.