By Will Dunham
WASHINGTON, Jan 26 (Reuters) – Using observations from the James Webb Space Telescope on a patch of sky covering nearly three times the area of the full moon, scientists have created the most detailed cosmic map yet of the mysterious substance called dark matter that accounts for most of what populates matter.
Simple matter makes stars, planets, people, and everything we can see. But it represents only 15% of all matter in the universe. The rest is dark matter, which does not emit or reflect light, making it invisible to the human eye and telescopes.
Scientists infer its existence based on large-scale gravitational effects, such as how fast galaxies rotate, how galaxy clusters are held together, and how light from distant objects bends as it passes through large cosmic structures.
The new map of the distribution of dark matter was based on this phenomenon of light bending – causing subtle distortions in the shape of about 250,000 distant galaxies as observed by Webb – thanks to the gravitational effects of matter along the line of sight.
Previous maps of dark matter were based on observations by the Hubble Space Telescope. The new map, powered by Webb’s massive capabilities, offers twice the resolution of previous maps, spans more parts of the universe and casts peers further back in time — effectively looking at the main period of galaxy formation, about 8 to 10 billion years ago.
“This allows us to better resolve dark matter structures, detect previously unseen mass concentrations, and extend dark-matter mapping to earlier ages of the Universe,” said observing cosmologist Diana Scognamiglio of NASA’s Jet Propulsion Laboratory in California.
The map reveals new details with unprecedented clarity of the vast structure of the universe known as the cosmic web – galaxy clusters, giant filaments of dark matter in which galaxies and gas are distributed, as well as regions of low mass density.
Webb, an infrared telescope with nearly six times the light-gathering power of Hubble, was launched in 2021 and operational in 2022.
“The James Webb Space Telescope is like putting on a new pair of glasses for the universe,” Scognamiglio said. “It sees fainter and more distant galaxies with much sharper detail than before. It effectively gives us a much denser grid of background galaxies to work with, which is what you want for this type of study. More galaxies and sharper images translate directly to sharper maps of dark matter.”
The map shows a section of the sky called the Cosmic Evolution Survey, or COSMOS, located in the direction of the constellation Sextans. The map will facilitate future exploration of the universe in several ways, the researchers said.
“For example, a key question in astrophysics is how galaxies grow and evolve over time — how the universe went from an almost perfectly homogeneous soup to the spectacular diversity of galaxies we see today,” said observational cosmologist and study co-author Jacqueline McCleary.
“Dark matter halos – self-gravitating ‘clouds’ of dark matter – are the sites of galaxy formation, the nurseries of galaxies, if you will. So knowing where the dark matter is, how much there is, and relating it to the population of galaxies within the dark matter distribution provides an important constraint and links the model state of the McGalaxy model and the state of the galaxy.
The researchers discovered the distribution of dark and ordinary matter using a method involving the bending of light.
The researchers said their observations are consistent with the leading cosmological model — called Lambda-CDM, or cold dark matter — that explains the evolution and composition of the universe after the Big Bang. The model posits that the universe is composed of dark matter and an invisible cosmic force called dark energy that is responsible for its rapid expansion.
“In this framework, dark matter provides the gravitational backbone upon which galaxies, groups and clusters form, creating large-scale cosmic webs. Our map provides a very sharp observational view of this dark matter scaffolding,” said Scognamiglio.
(Reporting by Will Dunham; Editing by Daniel Wallis)
