The Universe’s Oldest Light Reveals Unprecedented Dark Matter Patterns

Scientists have used the oldest light in the universe to capture an unprecedented glimpse of the distribution of dark matter, an unexplained substance that accounts for most mass in the cosmos, around galaxies, reports a new study. 

Whereas previous observations have mapped out galactic dark matter patterns as far as 10 billion years ago, the new results push that frontier way back to 12 billion years ago. The achievement reveals potential challenges to the standard model of cosmology, a well-corroborated framework that explains much of the strange phenomena that has been observed in space.

Scientists led by Hironao Miyatake, a cosmologist at Nagoya University, have obtained “the first detection of the dark matter distribution” around galaxies during this early era of the universe, which “opens up a new window for constraining cosmological parameters,” according to a study published on Monday in the journal Physical Review Letters. 

The team was able to make this breakthrough with the help of the cosmic microwave background (CMB), the oldest observable light in the universe, which is generated by remnant heat from the Big Bang.

“Look at dark matter around distant galaxies?” said Masami Ouchi, a cosmologist at the University of Tokyo and co-author of the study, in a statement. “It was a crazy idea. No one realized we could do this. But after I gave a talk about a large distant galaxy sample, Hironao came to me and said it may be possible to look at dark matter around these galaxies with the CMB.”  

Dark matter is one of the biggest unsolved mysteries in science, in part because this weird substance does not emit detectable light. Scientists only know that dark matter exists because of its clear gravitational influence on “normal'' visible matter, such as the stuff that makes up stars, planets, and our bodies. If scientists were able to identify the nature of dark matter, it would fill in a major gap in our knowledge of the cosmos that could shed light on a host of other questions, such as the fundamental composition of the universe and the evolution of galaxies like our own Milky Way.

Dark matter is not evenly distributed around the universe, and clumps of it are usually coincident with massive objects made of regular matter such as galaxies. One way to understand how the distribution of dark matter has evolved over time, and therefore how it has influenced regular matter, is to use bizarre natural telescopes known as gravitational lenses. 

These lenses are created when massive objects, such as galaxy clusters, are located in front of even more distant objects from our perspective on Earth. The gravitational fields of these foreground objects warp the light from the background objects in such a way that it can be magnified hundreds of times over, enabling scientists to peer into distant corners of the universe that would be otherwise out-of-view.

These cosmic lenses have helped researchers map out the distribution of dark matter as far as ten billion years ago, but Miyatake and his colleagues have now pioneered a new technique that reaches back even farther. The team used the Subaru Hyper Suprime-Cam Survey, an astronomical project based atop Hawaii’s Mauna Kea, to spot a whopping 1.5 million lensed galaxies that existed 12 billion years ago. The researchers then combined those images with observations of the CMB captured by the European Space Agency’s Planck satellite. 

The approach revealed the subtle lensed distortions of the microwaves that make up this ancient light, allowing Miyatake and his colleagues to map out key dark matter patterns earlier in the universe than ever before. In addition to pushing these observational limits, the results hint at a slightly different value for a key cosmological measurement—essentially, the clumpiness of matter—compared to the standard model of cosmology. If this gap between observation and theory remains consistent in future studies, it could present a challenge to the model that might require the advent of new physics. 

“Our finding is still uncertain,” Miyatake said in the statement. “But if it is true, it would suggest that the entire model is flawed as you go further back in time. This is exciting because if the result holds after the uncertainties are reduced, it could suggest an improvement of the model that may provide insight into the nature of dark matter itself.” 

“I was happy that we opened a new window into that era,” he concluded.