Observations by NASA / European Space Agency’s Hubble Space Telescope and the European Southern Observatory’s very large telescope (VLT) in Chile have shown that some of the principles of how dark matter behaves may be missing.
This missing component may explain why researchers have discovered unexpected discrepancies between observations of dark matter concentrations in a sample of galaxy clusters and theoretical computer simulations of how dark matter should be distributed in clusters. New findings suggest 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 object forms a large part of the mass of the galaxy and forms the basis of the massive formation of our universe. Because dark matter does not emit, absorb, or reflect light, its presence is only known by the gravitational pull on the visible object in space. Astronomers and physicists are still trying to figure out what it is.
Galaxy clusters are the largest reservoir of dark matter. Clusters are made up of individual member galaxies that are largely held by the gravity of black matter.
“One of the characteristics of the real universe is that we are not capturing our current theoretical models,” said Natarajan, a priest at Yale University in Connecticut, USA. “This may indicate a gap in our current understanding of the nature of dark matter and its properties, as these outstanding data have allowed us to investigate the detailed distribution of dark matter on tiny scales.”
How is dark matter mapped?
The distribution of dark matter in clusters is mapped by measuring the bending of light – the gravitational lensing effect – that they produce. The gravity of a dark object concentrated in clusters extends light from distant backgrounds to objects. This effect distorts the shape of the background galaxies that appear in the images of the clusters. Gravitational lensing can often produce multiple images of galaxies at equal distances.
The higher the concentration of dark matter in the cluster, the more dramatic its light bending effect. The presence of small-scale clusters of dark matter associated with individual cluster galaxies increases the level of distortions. In some ways, the Galaxy cluster acts like a large-scale lens with many small lenses embedded inside it.
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What did the researchers find?
Hubble’s crisp images were taken by the tablescope’s wide-field camera 3 and the advanced camera for surveys. Together with VLT’s Spectra, the team created an accurate, highly loyal, dark-matter map. By measuring lensing distortions, astronomers can detect the amount and distribution of dark matter.
To the team’s surprise, in addition to the dramatic arts and elaborate features of distant galaxies produced by the gravitational lensing of each cluster, Hubble images also yielded an unexpected number of small arcs and distorted images, located near the core of each cluster, where the largest The galaxies remain. Researchers believe that nested lenses are formed by the gravity of dense concentrations of matter within individual cluster galaxies. Follow-up spectroscopic observations measured the velocity of stars orbiting within cluster galaxies to cut down their masses.
Combining Hubble imaging and VLT spectroscopy, astronomers were able to identify dozens of multiplied image, lens, background galaxies. This allowed them to assemble a properly-calibrated, high-resolution map of the mass distribution of dark matter in each cluster.
The team compared dark-matter maps with samples of simulated galaxy clusters with similar ones located at approximately equal distances. Clusters in the computer model do not show the concentration of any dark-matter of the same size on the scales associated with small-sized scales – individual cluster galaxies.
“With advanced cosmological simulations, we can match the quality of the observations analyzed in our paper, as we have never done in detail before,” said Stefano Borgani of the University of Digli Studi de Trist in Italy.
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