Art by Charlotte Leakey.
If you’ve ever read a schlocky sci-fi novel or tuned into an episode of
Cosmos, you’ve probably heard of dark matter, the mysterious sister to ordinary baryonic matter that makes up some eighty-five percent of our universe. So-called because it doesn’t interact with EM radiation or normal matter, dark matter has only ever been observed indirectly via its gravitational influence. What is it made of? No one is quite sure—candidate explanations range from new elementary particles to primordial black holes. Nearly all of the major schools of thought in the astrophysics community subscribe to a “cold dark matter” model, in which the constituent particles move slowly and larger structures emerge hierarchically from the bottom up. But, while the consensus CDM model has been very successful, there are still some inconsistencies with observation—and another big one has just emerged.