Webb Data Reveals Dark Matter

This image from NASA’s James Webb Space Telescope, containing nearly 800,000 galaxies, is superimposed on a map of dark matter, shown in blue. Brighter blue areas indicate a higher density of dark matter. The researchers used the Webb data to find dark matter – which is invisible – via its gravitational influence on ordinary matter.

The area of ​​sky shown here measures 0.54 square degrees (about 2½ times the size of the full Moon) and is located in the Sextans constellation. Webb’s Near Infrared Camera (NIRCam) scanned this region for a total of approximately 255 hours.

Dark matter does not emit, reflect, absorb or block light and is therefore not visible to the human eye or traditional telescopes. But it interacts with the universe through gravity, and large clumps or clumps of dark matter have enough mass to bend space itself. Light arriving at Earth from distant galaxies is slightly distorted as it passes through the curved fabric of space-time. In some cases, the distortion is large enough to be visible to the naked eye, almost as if the galaxy was seen through a distorted window, an effect called strong gravitational lensing. In the case of the dark matter map shown here, scientists inferred the distribution of dark matter by relying instead on an effect called weak gravitational lensing, which leads to much more subtle distortions of light from thousands of galaxies.

Dark matter in this area of ​​the sky was also mapped in 2007 using data from NASA’s Hubble Space Telescope. Webb’s map contains about 10 times more galaxies than maps of the area made by ground-based observatories and twice as many as Hubble’s map. It reveals new clusters 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 entire COSMOS “field” measures 2 square degrees (about 10 times the size of the full Moon) and has been photographed 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 develop and how dark matter influences their evolution. Only data from Webb and Hubble have been used to map dark matter in the region.

To refine distance measurements to many galaxies for the map, the team used Webb’s Mid-Infrared Instrument (MIRI), designed and managed during launch by the agency’s Jet Propulsion Laboratory, as well as other space and ground-based telescopes. The wavelengths detected by MIRI also make it suitable for detecting galaxies obscured by cosmic dust clouds.