Just as we need the electromagnetic force to tell us about protons, neutrons, electrons and the richness of all the particles we know of—collectively called the Standard Model of particle physics—we need more than gravity to unlock the secrets of the dark side. As a result, the past three decades of the search for dark matter have been characterized by null results. For most of that time, researchers have been looking for a single particle to explain dark matter.

Yet dark matter might not be one particular particle—it may be a whole hidden sector of dark particles and forces. In this dark sector, particles would interact through their own independent forces and dynamics, creating a hidden world of cosmology running parallel to our own.

There could be dark atoms—made of dark protons, dark neutrons and dark electrons—held together by a dark version of electromagnetism. The carriers of this force, the dark photons, might (unlike our photons) have mass, allowing huge dark atomic nuclei—so-called nuggets—to form. And the totally different dynamics of dark matter in this dark sector would have different effects on the evolution of normal matter throughout time. The interactions of nuggets in galaxies could help form supermassive black holes in the centers of galaxies, causing them to grow larger than they otherwise would.