Kathryn Zurek on a Surprising Twist in the Long Hunt for Dark Matter
This image shows the galaxy cluster Abell 1689, with the mass distribution of the dark matter in the gravitational lens overlaid (in purple). Credit: NASA/ESA
by Andrew Moseman
Two decades after Kathryn Zurek first joined the hunt for dark matter, we know a lot more about what we don’t know about the hidden side of the universe.
Zurek, a Caltech professor of theoretical physics, began her work at a time when dark matter physicists were focused on the weak force — which, despite its name, is stronger than gravity. This force appeared to be the key to unlocking the secrets of dark matter, the mysterious stuff whose gravitational effects can be observed and measured but which doesn’t seem to interact with the ordinary forms of matter we’re familiar with.
Zurek wasn’t convinced that an explanation would come from the weak force—to the point that she made a bet with another researcher, Dan Hooper of the University of Wisconsin–Madison, that an explanation for what dark matter is made of would not be soon in arriving. As she writes in a new Scientific American article, “Dark Matter Might Lurk in Its Own Shadow World,” she now feels that no one particle will explain this shrouded phenomenon.
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.