Stellar survey to reveal distribution of dark matter

Chuck Bednar for – @BednarChuck

A team of researchers from the National Astronomical Observatory of Japan (NAOJ) along with an international team of colleagues have started a new wide-area dark matter distribution survey that could help explain the role of dark energy in the expansion of the universe.

Using the using Hyper Suprime-Cam, a new wide-field camera installed on the Subaru Telescope in Hawaii, the NAOJ-led team conducted observations across an area of 2.3 square degrees in the skies near the constellation Cancer. They discovered nine large concentrations of dark matter, each of which was the mass of a galactic cluster, the Observatory said in a statement.

Surveying how dark matter is distributed, as well as how the distribution changes over time, is a key part of understanding how dark energy controls universal expansion. The results demonstrate that astronomers now have both the tools and techniques to understand dark energy, and the next step is to expand the survey to cover more than 1,000 square degrees.

The study is available online and has been published in The Astrophysical Journal. The research team was led by Dr. Satoshi Miyazaki of the NAOJ’s Advanced Technology Center and includes astronomers and astrophysicists from Princeton University and the University of Tokyo.

Using ‘weak lensing’ to study dark energy

Dr. Miyazaki, the lead developer of the HSC instrument, claims the key to understanding the properties of dark energy (and in turn the expansion of the universe) lies in mapping dark matter over a wide area. The results of their research thus far demonstrated that their current equipment and methodology is up to the task.

Using the HSC, the researchers are prepared to investigate how dark matter distribution has been changing over time, as well as conduct a detailed investigation into the expansion history of the universe. Since dark matter does not emit light and cannot be directly detected by telescopes, the team plans to seek out and analyze a phenomenon known as “weak lensing.”

Concentrated dark matter acts like a lens, bending light coming from even more distant objects. By analyzing how that background light is bent, and how the lensing distorts the shapes of those background objects, researchers can determine how dark matter is distributed in the foreground. This allows them to determine how it has assembled over time.

That knowledge can then be linked to the expansion history of the universe and reveal some of the physical properties of dark energy, its strength, and how it has changed throughout the years. To collect enough data to make this possible, astronomers need to observe galaxies more than a billion light years away across an area of more than 1,000 square degrees, which is now possible thanks to the combination of the Subaru telescope and the HSC instrument.

The HSC took a decade to develop, Dr. Miyazaki said, and has a field of view more than seven times larger than its predecessor. Using the instrument, the researchers have uncovered a greater number of galaxy clusters than predicted. If these findings hold up once the dark matter map is expanded, it could indicate that there is less dark energy as expected in the past, suggesting that the universe can expand gently and stars and galaxies can form quickly.


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