“Previously, we were looking at a blurry picture of dark matter. Now we’re seeing the invisible scaffolding of the universe in stunning detail, thanks to Webb’s incredible resolution,” said Diana Scognamiglio, lead author of the paper and an astrophysicist at NASA’s Jet Propulsion Laboratory in Southern California.
The new picture is not a photograph of a dark matter. It is an exact calculation of the location of gravity, by the manner in which the remote light reaches a telescope, having traversed billions of light-years of constructed space. Practically, it will be to make a lab in the sky of the dominant mass component in the universe, one that neither scatters nor screens light, but which leaves a signature on all that is bright.
The map is based on the COSMOS field a part of the constellation Sextans observed over the years in numerous facilities and now re-observed with Webb. The strip observed is approximately 2.5 times the size of the full Moon, and Webb spent approximately 255 hours observing the area and he was able to detect approximately 800,000 galaxies, many of which were never recorded before. The density is important since weak gravitational lensing is based on statistics: the more available background galaxies, the more clearly their subtle, coherent shape deformations are revealing the structure of the foreground mass distribution. The resulting dark-matter map creates a web-like pattern dense knots around the galaxy clusters and thinner strands between them due to uneven spread of gravity. It gathers, magnifies and systematizes. The reconstruction on the Webb is about twice as sharp as similar constructions during the Hubble era, and the COSMOS-Web data is deeper, providing more background galaxies to lense, allowing a finer structure to be seen where older surveys scattered it out.
The sharper form assists in distinguishing between the two concepts which are frequently confused in the popular accounts of the light as the tracker and mass as the designer. Dark matter has no emission, reflection, absorption, and blocking of light, and it travels through normal matter with little interaction. However, the new analysis reveals that its gravity and apparent matter are in a very close correspondence throughout the field, suggesting a coevolution over a period of time and not just a chance overlay. The comparison, as described by Richard Massey, an astrophysicist at Durham University and an author of the research, actually appears like this: “Wherever we see a big cluster of thousands of galaxies, we also see an equally massive amount of dark matter in the same place. And when we see a thin string of regular matter connecting two of those clusters, we see a string of dark matter as well.”
Counting galaxies is not the only task that Webb has. Another procedure that was utilized by the team in order to refine distance estimates of many galaxies is the Mid-Infrared Instrument (MIRI) used by Webb, a process that enhances the way lensing signals are assigned along the line of sight. IR sensitivity is also useful in rediscovering galaxies that are partially obscured by dust to reduce selection biases that are susceptible to propagating into an astronomical mass map. Further advances in analysis are set to make this field an anchor of calibration: a well-characterized patch of reference against which future wide-area reconstructions can be calibrated.
The engineering accomplishment is not only resolution, in the long perspective, but scalability. The identical gravitational method can be scaled up a notch beyond a deep, extensive, and scrutinized window such as COSMOS out to much greater scales at the cost of spatial acuity. The paper indicates that as a next step, the mapping of the dark matter is going to be expanded with the help of the Euclid telescope offered by ESA and the Nancy Grace Roman Space Telescope offered by NASA.
The value of maps as they get broader and increasingly sharp is cumulative: the more a lensing reconstruction is refined the closer the bond between the galaxy positions and the positions of gravity: the more they make the “invisible” visible.
