Distorted images of distant background galaxies embedded within the cluster, which are seen as curves and smear features. The dark matter model also predicts that there should be more dwarf satellite galaxies around the Milky Way and more diffuse than they exist.
The new study, performed by an worldwide team of researchers, took advantage of a phenomenon called gravitational lensing. Galaxies in the three withdrawals are examples of these effects. Gravitational lensing can often also produce multiple images of the same distant galaxy. The red dots around the galaxy in the upper left indicate an emission from hydrogen clouds at one distant source. These blobs were detected by the Multi-Unit Spectroscopic Explorer (MUSE) at the European Southern Observatory's Very Large Telescope (VLT) in Chile. Dots do not appear in Hubble images. Over time, the continued draw of gravity pulled galaxies together, forming large clusters.
Image credit: NASA, European Space Agency, b. The interplay between dark and luminous matter in dense cosmic environments, such as galaxy clusters, is studied theoretically using cosmological simulations. Dark matter does not absorb, reflect, or emit any electromagnetic radiation which makes it completely undetectable in a direct way. Its existence is only known by its attractiveness to the visible matter in space. Using these kinds of data, astronomers can build computer simulations to estimate dark matter concentrations in the universe.
Of course, astronomers can't actually see these dark-matter halos, but they can see the way in which these invisible blobs can bend light.
"Galaxy clusters are ideal laboratories in which to study whether the numerical simulations of the Universe that are now available reproduce well what we can infer from gravitational lensing", Massimo Meneghetti, a researcher at the Astronomical Observatory of Bologna and lead author of a new study, said in a Hubble press release. Again, subtracting away the visible matter will leave you with how much dark matter there is.
The gravitational pull of cold dark matter in galaxy clusters can distort or bend the light coming from distant background galaxies, in a phenomenon called gravitational lensing. And, by zooming in, we can see how dark matter should be distributed in the area of individual galaxies. Dark matter in clusters is therefore distributed on both large and small scales.
"Galaxy clusters are ideal laboratories in which to study whether the numerical simulations of the universe that are now available reproduce well what we can infer from gravitational lensing", lead author Massimo Meneghetti of the INAF-Observatory of Astrophysics and Space Science of Bologna in Italy said in the statement. From Bologna, Italy, lead author of the study. "We have done a lot of testing of the data in this study, and we are sure that this mismatch indicates that some physical ingredient is missing either from the simulations or from our understanding of the nature of dark matter", Meneghetti said. "But we don't yet know whether this is telling us something about our computations and simulations, or whether it's telling us something fundamental about dark matter".
"To me personally, detecting a gnawing gap - a factor of 10 discrepancy in this case - between an observation and theoretical prediction is very exciting", said astrophysicist Priyamvada Natarajan of Yale University. "This could signal a gap in our current understanding of the nature of dark matter and its properties, as this exquisite data has permitted us to probe the detailed distribution of dark matter on the smallest scales". Dark on the smallest scales.
The research is described in a paper published today (Sept. 11) in the journal Science. The peaks are the dollops of dark matter associated with individual cluster galaxies. The higher the concentration of dark matter in the cluster, the more dramatic the bending of the light.
The clear Hubble images, along with spectra from the VLT, helped the team produce an accurate, high-resolution map of dark matter.
By combining Hubble imaging and VLT spectroscopy, the astronomers were able to identify dozens of multiply imaged, lensed, background galaxies. These small scale clumps of dark matter enhance the overall distortion.
The three major galaxy clusters used in the analysis, MACS J1206.2-0847, MACS J0416.1-2403, and Abell S1063 were part of two Hubble scans: boundary fields and cluster lens scanning and supernova using Hubble (Clash) software.
To test those predictions, the researchers used images from the Hubble Space Telescope to map a large collection of galaxies and all objects around them. Therefore, the researchers made a decision to use gravity lensing to determine whether the distribution of the dark matter found in the samples is applicable to the locations we see through gravity lensing. "Based on our spectroscopic study, we were able to associate the galaxies with each cluster and estimate their distances", said team member Piero Rosati of the University of Ferrara in Italy.
The team then took this high-fidelity data and compared it to theory-based computer simulations of clusters with similar masses and at comparable distances.
Future missions like the Nancy Grace Roman Space Telescope, set to launch in the mid-2020s, will use gravitational lensing of large galaxy clusters to find even more distant galaxies. Impatient theoretical cosmologists will undoubtedly test dark matter transformations long before further reanalysis emerges.