An international team of scientists has collaborated to create the deepest and most precise map of dark matter in the universe.
The cosmic map used the first year data from the Hyper Suprime-Cam (HSC) survey, an 820-megapixel camera attached to the Subaru telescope in Hawaii. The researchers also used the existing measurement from the European Space Agency's (ESA) Planck satellite.
The study was made available online on Sept. 24 via arxiv.org.
Dark Matter
Scientists believe that roughly 27 percent of the universe is made up of dark matter. While they cannot be seen, their presence is felt via its gravity, tugging on stars and galaxies as they travel through the cosmos.
When light travels from distant stars to Earth, the gravitational pull of other matters in its path — including dark matter — bends and distorts the light. This is called gravitational lensing and it is what the researchers from Japan, Taiwan, and the United States to create the "deepest wide field map of the three-dimensional distribution of matter in the universe."
Mapping Dark Matter
"Our map gives us a better picture of how much dark energy there is and tells us a little more about its properties and how it's making the expansion of the universe accelerate," explained Rachel Mandelbaum from Carnegie Mellon University, one of the authors of the study. "The HSC is a great complement to other surveys. Combining data across projects will be a powerful tool as we try uncover more and more about the nature of dark matter and dark energy."
The Subaru telescope allowed researchers to measure the gravitational distortion in 10 million galaxies, including those from very, very far away. Some images showed light from billions of years ago when the universe was still very young.
However, because light can also be bent or distorted by the atmosphere, the telescope, and the detector, the researchers also used data from images taken by the Hubble Space Telescope. They removed shape distortions caused by any other factors except gravitational lensing.
The researchers also use their cosmic map to infer how much dark energy, which has something to do with the universe's expansion, there is in the universe and where they are. They compared their findings to the fluctuations predicted by Planck satellite's observation of cosmic microwave background radiation left behind by the Big Bang. They found that the HSC provided mostly consistent but slightly lower measurements with the Planck's, which begs the question: does dark energy behave the way scientists believe it does?
The HSC survey will continue to collect data in the next four years. It is scheduled to complete its survey of the universe in 2020.
