Astronomers shed new light on mysterious dark matter

A new analysis by an astronomer with the University of Hawaiʻi Institute for Astronomy and collaborators from the University of Chicago is shedding new light on the amount of dark matter in the universe.

UH astronomer Eric Baxter co-authored the research that traces the mass distribution in the universe in three dimensions. The updated analysis was recently published in Physical Review D and shows there is six times as much dark matter in the universe compared to visible matter — a finding that was already well-known. However, the team also found that the matter is not as clumpy as previously expected when compared to the current best model of the universe.

For decades, cosmologists have mapped the distribution of mass in the universe, visible material and the mysterious dark matter, in an effort to improve the understanding of these fundamental building blocks. Baxter and his team claim their findings could add to a growing body of evidence that there might be something missing from the existing standard model.

“It seems like there are slightly less fluctuations in the current universe than we would predict, assuming our standard cosmological model anchored to the early universe,” Baxter said in a press release. “The high precision and robustness to sources of bias of the new results present a particularly compelling case that we may be starting to uncover holes in our standard cosmological model.”

Baxter and his team, which included Chiway Chang and Yuuki Omori from the University of Chicago and more than 150 international collaborators, complied their data using two different sky surveying methods and observations from 2008 to 20011. They were able to obtain new and high-precision constraints on the matter distribution of the universe across a wide range of cosmic history.

The team used the Dark Energy Survey, an astronomical survey designed to constrain the properties of dark energy. It uses visible light to map the distribution of galaxies. Data was also collected using the South Pole Telescope, which can map matter beyond the reach of galaxy surveys. The telescope operates at microwave frequencies and maps the relic radiation from the Big Bang known as cosmic microwave background.

Combining these two methods of looking at the sky not only increases the volume of the universe that can be probed, it also reduces the chance that results are thrown off by an error or bias in one of the forms of measurement.

“It functions like a cross-check, so it becomes a much more robust measurement than if you just used one or the other,” said Chang, an astrophysicist at the University of Chicago, in the press release.

But determining whether hints of problems in the standard cosmological model are real or just chance fluctuations will require more data.

The Dark Energy Survey has three years of data waiting to be analyzed, and the South Pole Telescope is performing a new survey of the cosmic microwave background with dramatically improved sensitivity. A third telescope, the Atacama Cosmology Telescope, is also currently undertaking a new high-sensitivity survey of the cosmic microwave background.

By combining these new and improved data sets, researchers expect to obtain dramatically tighter constraints on possible departures from the standard cosmological model in the near future.