Observations by NASA / European Space Agency Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope (VLT) in Chile have found that some theories may be missing from how dark matter behaves.
This missing component may explain how researchers have uncovered an unexpected discrepancy between dark matter concentrations in theoretical samples of large-scale galaxy clusters and theoretical computer simulations of how dark matter should be distributed across clusters. New findings indicate that some small-scale concentrations of dark matter produce lensing effects that are 10 times stronger than expected.
Dark matter is the invisible glue that holds stars, dust, and gas together in a galaxy. This mysterious substance forms the bulk of the mass of a galaxy and forms the foundation of the massive structure of our universe. Because dark matter does not emit, absorb, or reflect light, its presence is known only through its gravitational bridge over a visible matter in space. Astronomers and physicists are still trying to explain what it is.
Galaxy clusters are the largest repositories of dark matter. The clusters are made up of individual member galaxies that are largely held together by the gravity of dark matter.
One of the senior theorists on the team, Priyamvada Natarajan of Yale University in Connecticut, USA, said, “There is a feature of the real universe that we are not capturing in our current theoretical model.” “This may indicate a difference in our current understanding of the nature of dark matter and its properties, as these exquisite data have allowed us to examine the broadest distribution of dark matter at the smallest scale.”
How dark is the matter?
The distribution of dark matter in bunches is mapped by measuring the bending of light – the gravitational lensing effect – that they produce. The gravity of dark matter concentrated in bunches increases and heats the light from distant background objects. This effect produces distortions in the shape of background galaxies that appear in the images of clusters. Gravitational lensing can often produce multiple images of the same distant galaxy.
The higher the concentration of dark matter in a cluster, the more dramatically it has a light-bending effect. The presence of small-scale clumps of dark matter associated with individual cluster galaxies increases the level of deformations. In some sense, the galaxy cluster acts as a large-scale lens with several small lenses embedded within it.
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What did the researchers find?
Hubble’s crisp images were taken for survey by Telescope’s Wide Field Camera 3 and Advanced Camera. Coupled with spectra from VLT, the team produced an accurate, high-fidelity, dark-matter map. By measuring lensing distortions, astronomers can detect the volume and distribution of dark matter.
To the team’s surprise, in addition to the dramatic arcs and elongated features of distant galaxies created by the gravitational lensing of each cluster, the Hubble images also revealed an unexpected number of unexpected small-sized arcs and distorted images near the core of each cluster, Where galaxies reside on the largest scale. Researchers believe that nested lenses are formed by gravity of dense concentrations of matter inside individual cluster galaxies. Subsequent spectroscopic observations measured the velocities of stars orbiting inside several sky Ganges, which reduced their mass.
By combining Hubble imaging and VLT spectroscopy, astronomers were able to identify dozens of multiply, lensed, background galaxies. This allowed them to assemble a well-calibrated, high-resolution map of the mass distribution of dark matter in each cluster.
The team compared Dark Matter maps with samples of equally spaced simulated galaxy clusters with similar mass. Clusters in the computer model did not show the same levels of small-scale dark-matter concentration – scales associated with individual cluster galaxies.
“With Universitas cosmological simulations, we can match the quality of the observations analyzed in our paper, never allowing detailed comparisons,” said Stefano Borgani of the Universita deli Studi de Trieste, Italy.
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