An international team of researchers led by Rachel Mandelbaum of Carnegie Mellon University has been able to create the most detailed and extensive map of the three-dimensional distribution of matter in the Universe, and, using Hyper Suprime-Cam (HSC) data, significantly increased the range of human knowledge about dark energy. The study was sent for publication by the Astronomical Society of Japan.
The modern Universe is a collection of various locations. As the universe has expanded over the past 14 billion years, galaxies and dark matter are continually coalescing under the influence of gravity, creating an even more fragmented landscape with denser clumps of matter and huge voids.
The force of gravity that pulls matter together also affects how we can observe astronomical objects. When light travels from distant galaxies to Earth, the gravitational pull of other matter in its path, including dark matter, bends the light. As a result, the images of galaxies that telescopes show us are slightly distorted – a phenomenon called weak gravitational lensing. Within these distortions there is a large amount of information, a storehouse of knowledge for scientists who seek to better understand the distribution of matter in the Universe and find a definition of the nature of dark energy.
The HSC map, based on data from the Japanese Subaru telescope in Hawaii, allowed researchers to measure gravitational distortion in images of about 10 million galaxies.
The Subaru Telescope has allowed scientists to see galaxies again in time much better than in previous observations. For example, the Observation Mission Dark Energy Survey allowed a much larger area of the sky to be analyzed with a similar level of accuracy than the HSC, but it only covered the nearby universe. Although the HSC has a narrower range, its view is more detailed, allowing researchers to see fainter galaxies and to make a clearer map of the distribution of dark matter.
The research team compared their map to the fluctuations provided by satellite observations from the Planck space agency from the earliest days of the universe. The HSC measurements were slightly worse, but still statistically consistent with Planck's observations. The fact that HSC and other lax lensing studies are finding lower results than Planck raises in the scientific community the nagging question of whether dark energy really behaves like Einstein's cosmological constant.
“Our map gives us a better idea of how much dark energy exists and tells us a little more about its properties and how it accelerates the expansion of the universe,” Mandelbaum said. 'HSC is a great addition to other observations. Combining project data will be a powerful tool and allow us to uncover much more about the nature of dark matter and dark energy. '
Measuring distortion caused by weak gravitational lensing is not an easy task. The effect is quite small, and distortions in galactic forms can also be caused by the atmosphere, telescope, and detector. To get accurate results, researchers need to know that they are only measuring the effects of weak lensing.
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 detailed simulations of the HSC survey data from images from the Hubble Space Telescope. With these models, they were able to apply shape corrections to the galaxy to remove shape distortions caused by effects other than lensing.
The presented result is the result of work from the beginning of the mission. If the HSC study collects data over five years, it will provide even more information about the behavior of dark energy, as well as provide new data on the evolution of galaxies and massive clusters of galaxies in outer space, will allow the study of objects such as supernovae, to study in more detail our own galaxy, the Milky Way.
