Scientists confounded by new findings on universe's mysterious dark matter

Gravitational lensing

Gravitational lensing

But according to a new study, some tiny clusters are distorting space much more than scientists had expected. It warps and magnifies the light of distant background galaxies beyond the cluster.

"Galaxy clusters are ideal laboratories to understand if computer simulations of the universe reliably reproduce what we can infer about dark matter and its interplay with luminous matter", Massimo Meneghetti, a cosmologist at the National Institute for Astrophysics in Italy and lead author on the new research, said in the statement.

These formations also contain a lot of dark matter - not only because it binds them together, but because the individual galaxies they're comprised of contain dark matter, too. Models of the early universe formed galaxies and galaxies by creating structures made of dark matter. The fact that these models get the big picture so right has been a strong argument in their favor.

This suggests there is something missing from our understanding of dark matter.

So, one of the ways astronomers can detect dark matter is through gravitational lensing, in which gravity essentially distorts space.

This effect in space that results from a star or even a galaxy curving space and thus bending the path of light as it passes the object. Depending on the exact details of how the objects are arranged, the result can be anything from a simple magnification to a circular ring, or an object appearing multiple times.

The recently found concentrations intrigue scientists, and they might need some extra work to figure everything out. This is one of the many sources that support the dark side. Or at least, that's what a research team thinks. The researchers claimed that the simulation shows that "dark matter clusters together in halos connected by long filaments", adding that gas gets funnelled via filaments and gets collected and forms into galaxies, stars and planets. These models, as they move forward, provide an explanation of how the distribution of that dark object should have been at different points in the history of the Universe up to the present.

If we could see dark matter, it might look like what researchers call the cosmic web - essentially interconnected filamentary scaffolding where galaxies can form.

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Because a higher concentration of dark matter in a cluster gives a more dramatic light-bending effect, the team surmised that the presence of the nested lenses were being produced by the gravity of dense pockets of dark matter inside the individual cluster galaxies that had magnified and warped the passing light. The additional gravitational pull at the points where filaments intersected would draw in regular matter, leading to the first galaxies. Once again, subtract the visible matter, et voila - a map of the dark matter within that lensing cluster.

New data obtained from the Hubble Telescope indicates that concentration of dark matter is much higher in several galaxies, by over an order of magnitude.

Meanwhile, in the real universe ...

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. Subsequent imaging using a very large telescope helped to identify the distance of an object based on how much light traveled to the red end of the spectrum by the expansion of the universe.

When the team sat down to analyse the data, they found the large-scale lensing effects as expected to be produced by the galaxy as a whole. The researchers found a strong agreement between the appearance of lensed objects and the location of individual galaxies, which allowed them to validate their mass-distribution calculations.

The researchers then built 25 simulated clusters using the space simulator and performed similar analyzes on the clusters.

The two do not match. There were significantly more areas that generated high distortion in the real-Universe galaxy than there were in the model. This discovery could help astronomers gain more insight into dark matter in the future.

This is not the first kind of discrepancy we've seen. Dark matter models also predict that there should be more dwarf satellite galaxies around the Milky Way and that they should be more diffuse than they are. But even the slightest hold we do possess might be missing a significant thing. So, rather than finding two problems that could both be solved by making one adjustment, the two issues appear to need adjusting in opposite directions. "One possible reason for this discrepancy is that we might miss some basic physics in the simulations". Since both of those get the big picture of the Universe largely right, however, the issue is going to be a subtle one and consequently hard to identify, should these results get an independent confirmation. If there is something more complicated, it could easily throw out the models. Using this map, and focusing on three key clusters - MACS J1206.2-0847, MACS J0416.1-2403, and Abell S1063 - the researchers tracked the lensing distortions and from there traced out the amount of dark matter and how it is distributed.

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