The Hyper Suprime-Cam investigation maps dark matter in the universe

Today, an international group of researchers, including Rachel Mandelbaum, of Carnegie Mellon University, has released the most comprehensive three-dimensional map of the three-dimensional distribution of matter in the universe. (HSC).

The current universe is a very lumpy place. While the universe has developed over the past 14 billion years, gravity has increasingly brought galaxies and dark matter together, creating an agglomerated landscape with large aggregates of matter. separated by little or no important gaps.

The gravity that attracts matter also influences the way we observe astronomical objects. While light travels distant galaxies to the Earth, the gravitational attraction of the other matter in its path, including dark matter, bends the light. As a result, images of galaxies that telescopes see are slightly distorted, a phenomenon called a low gravitational lens. Among these distortions, there is a large amount of information that researchers can extract to better understand the distribution of matter in the universe and provide clues to the nature of dark energy.

The HSC map, created from data collected by the Subaru Japanese telescope in Hawaii, allowed researchers to measure gravitational distortion on images of about 10 million galaxies.

The Subaru telescope allowed them to see galaxies farther back in time than in other similar surveys. For example, the Dark Energy Survey analyzes a much larger area of ​​the sky with a level of precision similar to that of the HSC, but only monitors the nearby universe. HSC takes a closer but deeper view, which has allowed researchers to see weaker galaxies and map the distribution of dark matter more accurately.

The research team compared their map with the fluctuations predicted by the Planck satellite observations of the European Space Agency on the background radiation of cosmic microwaves – the radiation of the early days of the day. universe. The CSH measurements were slightly lower than those of Planck, but still statistically compatible. The fact that HSC and other weak-lensed surveys give slightly lower results than Planck raises the fascinating question of whether dark energy really behaves like Einstein's cosmological constant.

"Our map gives us a better idea of ​​the amount of dark energy present and tells us a little more about its properties and how it accelerates the expansion of the universe," Mandelbaum said. "The HSC is an excellent complement to other surveys, and combining data across projects will be a powerful tool to discover more and more the nature of dark matter and dark energy."

Measuring the distortions caused by the weak gravitational lens is not easy. The effect is quite weak and the atmosphere, the telescope and the detector can also cause distortions in the shapes of galaxies. For accurate and accurate results, researchers need to know that they only measure the effects of lenses.

Mandelbaum, an associate professor of physics and a member of the McWilliams Center for Cosmology at Carnegie Mellon, is an expert in controlling these external distortions. She and her team have created a detailed image simulation of HSC survey data based on images from the Hubble Space Telescope. From these simulations, they were able to apply corrections to the shapes of the galaxy to eliminate shape distortions caused by effects other than lenses.

These results come from the first year of data from the HSC survey. In all, the HSC survey will gather five years of data that will provide even more information on the behavior of dark energy and will target other objectives such as the study of the evolution of galaxies and massive clusters of galaxies. in the course of cosmic time. like supernovae, and even studying our own galaxy of the Milky Way.

The search will be uploaded to the preprint server arxiv.org and will be submitted for publication by the Japan Astronomical Society.

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