The Universe has an invisible skeleton made of particles we can’t describe in our current theories, known only as dark matter. Its strong gravity pulled everything else together inside it to form stars, galaxies, and eventually us. Discovering what dark matter is made of would fill an enormous gap in theories of subatomic physics and allow us to better understand how the Universe came to be. The axion, a theoretical particle proposed to solve another unrelated mystery, could be the answer. The search for axion dark matter is well underway with the Axion Dark Matter eXperiment, and our group at Stanford is expanding on that search with Volume Enhanced Resonators for Axions (VERA) by developing new axion detectors.

Since the 1960s there has been plenty of evidence to support the existence of dark matter through astrophysical and cosmological observations, and at this point we’re very confident that it exists. The question remains, though: what is dark matter actually made of? Weakly interacting massive particles (WIMPs)? Neutrinos? Primordial black holes? Or none of the above?