Scientists may have found another way to measure the distribution of dark matter. In a surprise finding, physicists from the Dark Energy Survey announced new evidence on the link between light and dark matter.
The study focused on intracluster light, a faint type of light found inside clusters of galaxies. Scientists think this light may provide a new way to measure dark matter—a mysterious form of matter that is invisible to telescopes, yet is thought to account for the vast majority of matter in the universe. What dark matter consists of stands as one of the major mysteries of modern cosmology.
“Just measuring the intracluster light itself is pretty exciting. The dark matter part is a bonus,” said Yuanyuan Zhang, an astrophysicist with the Kavli Institute for Cosmological Physics and Fermi National Accelerator Laboratory, who led the studies.
She noted that they were able to find the correlation thanks to the enormous amount of data they had from the Fermilab-hosted Dark Energy Survey—an international effort to map the sky and understand cosmic structure. Since the observations concluded in 2019, scientists have been poring over the data it collected, looking for patterns.
This research team was initially focused on measuring intracluster light. Intracluster light has long been suspected of possibly being a significant component of clusters of galaxies, but its faintness makes it difficult to measure. No one knows how much there is or to what extent it has spread through galaxy clusters. Its source appears to be rogue stars, those not gravitationally bound to any galaxy.
Most astrophysicists measure intracluster light at the center of a galaxy cluster, where it is brightest and most abundant. “We went very far away from the centers of the galaxy clusters, where the light is really faint,” Zhang said.
The observations suggested that intracluster light reflects both the total mass of a galaxy cluster and possibly also the distribution of dark matter.
Dark matter accounts for most matter in the universe—but it’s invisible to telescopes, so scientists know only that it differs greatly from the normal matter consisting of the protons, neutrons and electrons that dominate everyday life. We only know that it’s there because of the gravitational effects it has on things we can see, like stars and galaxies.
The team used such a technique, called weak gravitational lensing, to map the distribution of a galaxy cluster’s mass—including its dark matter. Then they compared that to the radial distribution of the intracluster light, i..e, how it changes as you move away from the center of a cluster.