Dark matter map reveals early Universe history

A new survey mapping dark matter is giving astronomers the techniques to understand more about dark energy and its role in the expansion of the Universe.

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A Hyper Suprime-Cam image with contour lines showing dark matter distribution. This mapping is key to understanding more about the Universe's expansion and dark energy's role in the process.
Credit: NAOJ/HSC Project

Astronomers are closer to understanding the nature of dark energy and its effect on the Universe through a new survey mapping the distribution of dark matter.

Researchers from the National Astronomical Observatory of Japan (NAOJ), the University of Tokyo and other institutions are adopting the Hyper Suprime-Cam, a wide-field camera installed on the Subaru Telescope in Hawaii, for the study.

Initial results from the survey, covering 2.3 square degrees on the sky towards the constellation Cancer, have revealed nine large areas of dark matter, each the mass of a galaxy cluster.

Hyper Suprime-Cam lead developer Dr. Satoshi Miyazaki from the National Astronomical Observatory of Japan's Advanced Technology Center, says: "Now we know we have both a technique and a tool for understanding dark energy. We are ready to use Hyper Suprime-Cam to create a 1,000 square degree dark matter map that will reveal the expansion history of the Universe with precise detail."

In the 1990s, studies showed that the Universe is expanding faster than it did in the past. Scientists explained the conundrum by inferring the existence of dark energy, which exerts a force that spreads galaxies apart and expands the Universe.

Dark matter is a substance that is directly undetectable, but which scientists have concluded exists because of its noticeable effect on the observable matter in the Universe. One technique to detect dark matter is analysing its effect on the light of a distant object as that light passes through it. This is called 'weak lensing'.

As dark matter makes up the majority of mass in the Universe, further detection and mapping of its distribution will help uncover the mysteries of dark energy. However, the amount of data needed to analyse dark energy would require observations of galaxies over a billion lightyears away, in an area larger than a thousand square degrees.

"This is why we spent 10 years to develop Hyper Suprime-Cam, a camera with the same of better image quality as Suprime-Cam, but with a field of view over seven times larger," says Miyazaki.

For this study, scientists analysed test data from the Hyper Suprime-Cam to see how it could map dark matter using weak lensing. A two-hour exposure covering 2.3 square degrees revealed clear images of various galaxies. This enabled the team to create a map of dark matter in the background by analysing the galaxies’ individual shapes.

The result was the discovery of nine areas of dark matter, each weighing as much a galaxy cluster. While this number exceeds predictions from current models of the early Universe, more research will be needed to confirm that the data is accurate.


 

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