Throwing light on how the structure of the universe unfolds, Inter-University Centre for Astronomy and Astrophysics (IUCCA) researcher Surhud More along with a team of astrophysicists and cosmologists have characterised the structure of dark matter in the Universe.
The team used the Subaru telescope in Hawaii and used the gravitational lensing effect to map the dark matter in the universe and how it is distributed around galaxies. Recently their paper got published in an international journal. The team measured a value for the ‘clumpiness’, of the universe’s matter.
Gravitational lensing experiments
There are three gravitational lensing experiments currently being conducted by scientists worldwide; the deepest amongst which is the Hyper Suprime-Cam (HSC) Survey carried out by this team. All of these surveys, independently, agree with each other and find less clumpiness in the dark matter distribution in the Universe today, than expected from the Cosmic Microwave Background (CMB).
According to Einstein's general relativity, light bends when it passes near a massive object, in a phenomenon known as gravitational lensing. Lensing causes the shapes of galaxies to be distorted by a tiny amount as the light from such galaxies travels through the Universe. Scientists had to measure these tiny changes imprinted on the shapes of galaxies. “Teasing out the gravitational lensing signal meticulously from images of millions of galaxies was quite a challenging task. Our team had to toil for many years in order to measure and model the signal”, said More who chairs the weak lensing working group of the HSC survey along with Hironao Miyatake, Associate Professor at Nagoya University.
“The simplicity of the standard cosmological model lies in the small number of parameters required to describe it”, said More. The density of dark matter in the Universe and the amount of clumpiness of matter, are quite important to understand how structure in the Universe evolves with time. “By mapping out dark matter in the Universe in a tomographic manner, that is in 3D, we are able to carry out a stringent test of the cosmological model”, he said.
Dark energy and dark matter make up 95% of our Universe today, but we understand very little about what they actually are and how they’ve evolved over the history of the universe. Cosmologists are eager to test the current model by constraining the few parameters that describe the standard model, such as by observing the fluctuations in the CMB, modelling the expansion history of the universe, or measuring the clumpiness of the universe in the relatively recent past.
Blind analysis of data
The team worked on four different independent but complementary ways to analyze the data. They spent roughly a year on the analysis. The unblinding of the results was quite a tense moment, as it was not known whether all four techniques would agree on their inferences. “It was both a moment of excitement and relief to see all the analyses yielding consistent results. The blinding procedure increases our confidence in the robustness of our results”, said More.
Huge survey with the world's largest telescope camera
The observations used one of the most powerful astronomical cameras in the world, the Hyper Suprime-Cam (HSC) mounted on the 8.2 m diameter Subaru Telescope on the summit of Maunakea in Hawai’i, a big island in the middle of the Pacific Ocean.
