Webb Data Reveals Dark Matter

This image from NASA’s James Webb Space Telescope, containing nearly 800,000 galaxies, is overlaid with a map of dark matter, represented in blue. Brighter blue areas indicate a higher density of dark matter. Researchers used Webb data to find the dark matter — which is invisible — via its gravitational influence on regular matter. The area of sky shown here is 0.54 square degrees (about 2½ times the size of the full Moon) and located in the constellation Sextans. Webb’s Near-Infrared Camera (NIRCam) peered at this region for a total of about 255 hours. Dark matter doesn’t emit, reflect, absorb, or even block light, and is therefore not visible to the human eye or traditional telescopes. But it does interact with the universe through gravity, and large clumps or clusters of dark matter have enough mass to curve space itself. Light traveling to Earth from distant galaxies becomes slightly distorted as it passes through the curved fabric of spacetime. In some cases, the warping is significant enough that it is apparent to the naked eye, almost as if the galaxy were being viewed through a warped windowpane, an effect called strong gravitational lensing. In the case of the dark matter map shown here, scientists inferred dark matter’s distribution by relying instead on an effect called weak gravitational lensing, which leads to much more subtle distortions of the light from thousands of galaxies. The dark matter in this area of sky was also mapped in 2007 using data from NASA’s Hubble Space Telescope. The Webb map contains about 10 times more galaxies than do maps of the area made by ground-based observatories and twice as many as Hubble’s map. It reveals new clumps of dark matter and captures a higher-resolution view compared to the Hubble map. Both the Hubble and Webb dark matter maps are part of a project called the Cosmic Evolution Survey (COSMOS). The full COSMOS “field” is 2 square degrees (about 10 times the size of the full Moon) and has been imaged by at least 15 telescopes in space and on the ground. Observing the same region with many different telescopes allows scientists to combine complementary views to understand how galaxies grow and how dark matter influences their evolution. Only Webb and Hubble data have been used to map dark matter in the region. To refine measurements of the distance to many galaxies for the map, the team used Webb’s Mid-Infrared Instrument (MIRI), designed and managed through launch by the agency’s Jet Propulsion Laboratory, along with other space- and ground-based telescopes. The wavelengths that MIRI detects also make it adept at detecting galaxies obscured by cosmic dust clouds. The James Webb Space Telescope is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency). Webb’s MIRI was developed through a 50-50 partnership between NASA and ESA. A division of Caltech in Pasadena, California, JPL led the U.S. contribution to MIRI. JPL also led development of MIRI’s cryocooler, done in collaboration with Northrop Grumman in Redondo Beach, California, and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. To learn more about Webb, visit: https://science.nasa.gov/webb