Dark matter might be even stranger than we thought, according to Hubble

Gravitational lensing

Gravitational lensing

The cluster contains distorted images of distant background galaxies, visible as arcs and speckled features. Models of the early universe formed galaxies and galaxies by creating structures made of dark matter. The presence of dark matter can explain the features of the cosmic microwave background.

In reality, the elusive and invisible dark matter that provides the universe with its structure accounts for most of the universe's mass. The fact that these models get the big picture so right has been a strong argument in their favor.

However, a new study suggests that the same model misunderstands the details at scale.

(Nanowerk News) Astronomers have discovered that there may be a missing ingredient in our cosmic recipe of how dark matter behaves. Or at least, that's what a research team thinks. Gravity distorts space itself and can do so by refracting light like a lens.

The gravitational lensing of a distant quasar by an intermediate body forms a double image seen by astronomers on Earth. Depending on the precise details of how the objects are arranged, the results can be anything from a simple magnification to circular rings or having the object appear multiple times.

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. In some cases, I even detected lenses with little problems. Dark matter models predict that there should be more dwarf satellite galaxies around the Milky Way and that they should be wider than they are.

The presence of something missing from our theories of dark matter and its behavior emerged from comparisons of observations of the dark matter concentrations in a sample of massive galaxy clusters and theoretical computer simulations of how dark matter should be distributed in such clusters. They also see how dark matter's gravity bends the fabric of spacetime, producing so-called "gravitational lenses".

According to this model, the universe was built hierarchically.

One of the reasons why scientists and researchers have been unable to know more about dark matter is that it doesn't interact with light. MACS J1206 is part of the Cluster Lensing and Supernova survey with Hubble (CLASH) and is one of three galactic groups that researchers studied with Hubble and VLT.

And indeed, galaxy clusters, in which thousands of galaxies are cloistered together, serve as distant laboratories for studying dark matter.

In order to discern visible matter from dark matter, the team then measured the velocity of the stars orbiting inside several of the cluster galaxies to get an estimate of each individual galaxy's mass.

The researchers believe that the embedded lenses are produced by the gravity of dense concentrations of dark matter associated with individual cluster galaxies.

Meanwhile, in the real universe ...

The researchers used images from NASA's Hubble Space Telescope, coupled with spectroscopy from the European Southern Observatory's Very Large Telescope, to produce high-fidelity dark-matter maps. Follow-up imaging using the Very Large Telescope helped identify the distance of those objects based on how much their light was shifted to the red end of the spectrum by the expansion of the Universe-the larger the redshift, the more distant the object. This allowed the researchers to determine which objects must be behind the galaxy cluster and, thus, potential candidates for gravitational lensing.

A software package then used the data to create a mass distribution for each galaxy cluster.

The researchers created 25 simulated clusters using the Universe simulator and performed a similar analysis with the clusters.

The two didn't match. Areas that make up more distortion in the real-universe galaxy were significantly larger than those in the model.

Dark matter can not be observed directly.

This is not the first contradiction of the type we have seen. This discovery could help astronomers gain more insight into dark matter in the future.

Composite image of the Perseus galaxy cluster using data from NASA's Chandra X-ray Observatory, ESA's XMM-Newton and Hitomi, a Japanese-led X-ray telescope. So, instead of finding two problems that can be solved with a single adjustment, it seems that you need to tweak both problems in opposite directions.

Researchers suggest that there are two possible explanations for this discrepancy.

Our understanding of dark matter and its behavior could be missing a key ingredient. However, since the big picture of the universe is largely correct for both, the problem would be subtle and consequently hard to identify if these results were confirmed independently. From this perspective, the mapped dark matter looks like a mountain range, with peaked regions. When more complex things happen, you can easily throw away the model. 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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