Researchers created the map, published Monday in the journal Nature Astronomy, by carefully measuring tiny changes in the shape of hundreds of thousands of galaxies imaged by the James Webb Space Telescope. This allowed them to reconstruct the locations of mass — including dark matter — and map the invisible structure of the universe, lead author Diana Scoganmiglio, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory, told Gizmodo in an email.
“We can’t see dark matter directly, so we map it by looking at how it bends light,” Scognamiglio explained. “As light from very distant galaxies travels toward us, it gets slightly distorted by the gravity of matter along the way.”
Dark matter as we’ve never “seen” it before
Astronomers believe that ordinary matter – particles that interact with light and are therefore observable – makes up only one sixth of all matter in the universe. The remainder is dark matter, which does not emit or absorb light. It interacts with the universe only through gravity.
According to the standard model of cosmology, dark matter must exist to explain certain gravitational effects, such as galaxies rotating unexpectedly fast or the fact that they are bound together more tightly than they should be. The best way for scientists to “see” dark matter indirectly is to measure its gravitational effects.
Scoganmiglio and his colleagues used weak gravitational lensing to do exactly that – the subtle distortion of light from distant galaxies caused by the gravity of the intervening mass.
High-resolution JWST images from the COSMOS-Webb survey allowed the team to measure the sizes of 129 galaxies per square arcminute and reconstruct a matter map with an angular resolution of about 1 arcminute – more than twice the resolution of earlier Hubble Space Telescope maps.
“JWST gives us much sharper images and lets us see fainter, more distant galaxies than other telescopes like Hubble,” Scognamglio said. “This means we have many more background galaxies to work with, and we can measure their sizes more accurately. More galaxies and faster images directly translate into a faster map.”
The brightest areas of the map mark places where large amounts of mass are concentrated, usually indicating giant galaxy clusters. The faint, thread-like features connecting these bright spots reveal giant filaments that link galaxies together, while darker, smoother regions show where relatively little matter is present.
“In simple terms, the map is a picture of the scaffolding of the universe,” Scognamiglio said.
A window into deep cosmic history
The extraordinary resolution of this new map not only provides an extremely detailed view of the structure of the universe, but it also allows astronomers to observe the structure much farther back than in previous maps.
It detects dark matter from the era when galaxies were most actively forming, and therefore provides a benchmark for testing models of the nature of dark matter as well as the galaxy environment during peak cosmic star formation about 8 to 11 billion years ago.
“The map is consistent with our current cosmological models, which predict that dark matter forms a web-like structure within which galaxies grow,” Scognamiglio said. “With this faster approach, we can test those predictions more precisely and look for small differences that might indicate new physics, such as alternative dark matter properties or subtle departures from standard gravity.”
They hope their map will pave the way for new research into how galaxies are affected by their dark matter environments. “We can now investigate how star formation, galaxy evolution and quenching occur [the shutting-down of star formation] It depends on where the galaxies are located within filaments and clusters,” Scognamiglio explained.
The quality of the data also opens the door to studying how matter evolves over time, he said. This will help Scognamiglio’s next project: creating a three-dimensional map of the mass of the universe. Next-generation space telescopes such as NASA’s Nancy Grace Roman and the European Space Agency’s Euclid will support this work by producing high-resolution data that cover much larger areas of the sky.
“JWST shows us what’s possible at ultra-high resolution, while those missions will extend it to cosmic volumes,” Scognamiglio said.
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