Physicists trying to understand the fundamental structure of nature rely on consistent theoretical frameworks that can explain what we see and simultaneously make predictions that we can test. On the smallest scale of elementary particles, the standard model of particle physics provides the basis of our understanding.
On the scale of the cosmos, much of our understanding is based on "standard model of cosmology". Informed by Einstein's theory of general relativity, it posits that the most of the mass and energy in the universe is made up of mysterious, invisible substances known as dark matter (making up 80% of the matter in the universe) and dark energy.
Over the past few decades, this model has been remarkably successful at explaining a wide range of observations of our universe. Yet we still don't know what makes up dark matter – we only know it exists because of the gravitational pull it has on galaxy clusters and other structures. A number of particles have been proposed as candidates, but we can't say for sure which one or several particles make up dark matter.
Now our new study – which hints that extremely light particles called neutrinos are likely to make up some of the dark matter – challenges our current understanding of its composition.