Invisible scaffolding: This image reveals the distribution of dark matter in the supercluster Abell 901/902, composed of hundreds of galaxies. The four highlighted areas indicate where dark matter is pooled into dense clumps, said experts.

Credit: NASA, ESA, C. Heymans, M. Gray, M. Barden.

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NEW YORK: Astronomers are getting their first detailed glimpse of how clusters of galaxies and dense clouds of dark matter interact to form some of the most colossal structures in the universe.

Dark matter is an invisible form of matter that physicists think makes up the bulk of the universe's mass. While it can't yet be directly detected, they have inferred its existence based on the effect its gravity has on surrounding normal matter and light.

First of a kind

Now, using NASA's Hubble Space Telescope, an international team of astronomers simultaneously mapped the invisible dark matter "scaffolding" of the galaxy supercluster Abell 901/902 in addition to the positions of hundreds of individual galaxies contained within.

The team was led by Catherine Heymans and Meghan Gray, of the University of British Columbia in Canada and the University of Nottingham in the United Kingdom, respectively.

The resulting map – presented last week in Texas at the annual meeting of the American Astronomical Society – is the highest resolution picture of dark matter created to date, and supports the idea that dark matter plays an important role in determining the positions and structures of galaxies in the universe.

"For the first time we are clearly detecting irregular clumps of dark matter in a supercluster," Heymans said. "Previous studies were only able to detect fuzzy, circular clumps, but we're able to resolve detailed shapes that match the distribution of galaxies."

The images revealed four main areas in the supercluster where dark matter was pooled into dense clumps. These clumps precisely matched the location of hundreds of old galaxies whose distorted shapes hint at violent collisions and mergers with one another in the deep past as they journeyed from the outskirts of the supercluster to the more crowded regions within.

Filling in the gaps

"We've known for a long time that galaxies in crowded environments tend to be older, redder, and rounder than those in the field," Gray said. "Galaxies are continually drawn into larger and larger groups and clusters by the inevitable force of gravity as the universe evolves."

Gray likens the new Hubble map of the supercluster to a profile of New York City that includes information about both its infrastructure and its people:

"We're examining large-scale features, like mapping the roads, counting skyscrapers, monitoring traffic," she explained. "At the same time we're also studying the residents to figure out how the lifestyles of people living downtown differ from those out in the suburbs. But in our case the city is a supercluster, the roads are dark matter, and the people are galaxies."