Dark matter just keeps getting darker. Although we see evidence of it throughout the universe, scientists have not yet figured out what it is. So they’re expanding their searches — and their ideas.
Dark matter appears to make up about 85 percent of all the matter in the universe. It produces no detectable energy. But it reveals itself by exerting a gravitational pull on the visible matter around it. In particular, we see its influence on most galaxies and clusters of galaxies. The dark matter acts as a sort of cosmic “glue” — its gravity holds the galaxies and clusters together.
For a long time, the leading idea has been that dark matter consists of WIMPs — particles that are many times heavier than a proton. These particles would seldom interact with any form of matter, including other WIMPs. Yet despite years of searching, with ever-increasing sensitivity, scientists haven’t found a single one. They’re still looking, but they’re also thinking about other possibilities.
One is called SIMPs — particles that are less massive than a proton. They’d be an unusual form of matter, and they would interact with each other more often than WIMPs would. Scientists are trying to produce them with the Large Hadron Collider and other particle accelerators.
They’re also looking for particles called axions — particles that are even lighter than SIMPs.
So far, though, dark matter remains elusive — it’s still a dark mystery.