Will Dunham
WASHINGTON (Reuters) – Using observations from the James Webb Space Telescope across a sky covering almost three times the area of the full moon, scientists have created the most detailed map of the universe yet, showing a mysterious substance called dark matter that makes up most of the matter in the universe.
Ordinary matter makes up stars, planets, humans, and everything else we can see. But it only makes up about 15% of all matter in the universe. The rest is dark matter, which does not emit or reflect light, so it is invisible to the human eye and telescopes.
Scientists infer its existence based on the gravitational effects it exerts over large areas, such as how fast galaxies spin, how clusters of galaxies fit together and how light from distant objects bends as it passes through the vast cosmic structure.
The new dark matter map is based on this light-bending phenomenon, which causes the shapes of some 250,000 distant galaxies observed by Webb to subtly distort due to the gravitational effects of matter along the line of sight.
Previous dark matter maps were based on observations from the Hubble Space Telescope. The new map, powered by Webb’s greater power, offers twice the resolution of the previous map, covers more of the universe, and goes back much further in time – effectively back to about 8 to 10 billion years ago, a critical period in galaxy formation.
“This allows us to resolve finer dark matter structures, detect previously unseen mass concentrations, and extend dark matter mapping to the early epochs of the universe,” said Diana Scognamiglio, an observational cosmologist at NASA’s Jet Propulsion Laboratory in California and lead author of the study published Monday in the journal Nature Astronomy.
The map reveals new details with unprecedented clarity about the macroscopic structure of the universe known as the cosmic web—clusters of galaxies, giant filaments of dark matter along which galaxies and gas are distributed, and regions of less mass density.
The Webb Infrared Telescope, which has about six times the light-gathering power of Hubble, will be launched in 2021 and will be operational in 2022.
“The James Webb Space Telescope is like putting a new pair of glasses on the universe,” Skognamario said. “It sees galaxies that are fainter, more distant, and with sharper detail than ever before. This actually gives us a denser grid of background galaxies, which is what this kind of study needs. More galaxies and sharper images translate directly into a sharper picture of dark matter.”
The map covers a portion of the sky called the Cosmic Evolution Survey (COSMOS) located in the direction of the sextant constellation. Researchers say the map will facilitate future studies of the universe in a number of ways.
“For example, a major question in astrophysics is how galaxies grow and evolve over time—how the universe went from an almost completely homogeneous soup to the spectacular variety of galaxies we see today,” said Jacqueline McCleary, an observational cosmologist at Northeastern University in Boston and study co-author.
“Dark matter haloes – self-gravitating ‘clouds’ of dark matter – are the places where galaxies form, the nurseries of galaxies, if you will. So understanding where and how much dark matter is, and relating that to the clusters of galaxies within, the distribution of dark matter sets important boundary conditions for models of galaxy formation and evolution,” McCleary said.
The method used by the researchers, involving the bending of light, revealed the distribution of dark matter and ordinary matter.
The researchers say their observations are consistent with a leading cosmological model called Lambda-CDM, or cold dark matter, which explains the universe’s beginnings with the Big Bang and its subsequent evolution and structure. The model holds that the universe is dominated by dark matter and an invisible cosmic force called dark energy, which is responsible for its accelerated expansion.
“In this framework, dark matter provides the gravitational backbone from which galaxies, clusters, and star clusters are formed, creating large-scale cosmic webs. Our map provides a clearer observational view of this dark matter scaffolding,” Skognamario said.
(Reporting by Will Dunham; Editing by Daniel Wallis)
