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While studying the Coma galaxy cluster in 1933, astronomer Fritz Zwicky uncovered a problem. The mass of all the stars

in the cluster added up to only about 1 percent of the heft needed keep member galaxies from escaping the cluster's

gravitational grip. He predicted that "missing mass," now known as dark matter, was the glue that was holding the

cluster together.

Dark matter, as its name implies, is matter that cannot be seen. It does not emit, absorb, or reflect light, nor does it interact with any known particles. It is even suspected to pass through particle accelerators without notice. The

presence of these elusive particles is only known through their gravitational pull on visible matter in space. This

mysterious substance is the invisible scaffolding of our universe that ties galaxies together in long filamentary

structures.

Even more confounding is that dark matter makes up the vast bulk of the mass in the universe. The stuff that stars, planets,

and humans are made of accounts for just a few percent of the universe's contents.

Astronomers have been chasing this ghostly material for decades but still don't have many answers. They have devised ingenious methods to infer dark matter’s presence by tracing the signs of its gravitational effects.

One method is by using gravitational lensing, in which the gravity of a massive galaxy cluster’s dark matter magnifies

and warps the light from a distant background object. This phenomenon produces smeared images of remote galaxies.

A recent study of three hefty galaxy clusters found that some small-scale concentrations of dark matter are so massive that

the lensing effects they produce are 10 times stronger than expected.

Researchers using the Hubble telescope and the European Southern Observatory’s Very Large Telescope in Chile discovered with unprecedented detail smaller-scale distorted images of remote galaxies nested like Matryoshka dolls within the larger-scale lens distortions in each cluster’s core, where the most massive galaxies reside.

This unexpected discovery means there is a discrepancy between these observations and theoretical models of how dark matter should be distributed in galaxy clusters. It could signal a gap in astronomers’ current understanding of the nature of dark matter and its properties.

Provider: Space Telescope Science Institute

Image Source: https://hubblesite.org/contents/news-releases/2020/news-2020-29

Curator: STScI, Baltimore, MD, USA

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