Based on images acquired by the Hubble space telescope and computer simulations, a team of scientists mapped the location of invisible "dark matter" in two very young galaxy clusters with unprecedented detail.

The researchers at the Johns Hopkins University said on Friday that their findings support the dark matter theory, which indicates the galaxies we can see form at the densest regions in the webs of invisible dark matter, just like froth gathers on top of ocean waves.

The team has published their work in the Dec. 10 issue of the Astrophysical Journal.

"Advances in computer technology now allow us to simulate the entire universe and to follow the coalescence of matter into stars, galaxies, clusters of galaxies and enormously long filaments of matter from the first hundred thousand years to the present," said Myungkook James Jee, co-author of the study.

"However, it is very challenging to verify the simulation results observationally, because dark matter does not emit light."

Using the Hubble telescope, the team observed two clusters, each containing more than 400 galaxies, in the southern sky. The clusters were forming when the universe was about half its present age.

The researchers measured the subtle gravitational "lensing" apparent in sharpened Hubble images to produce its detailed dark matter maps. The gravitational lensing means the small distortions of galaxies' shapes caused by gravity from unseen dark matter.

The result of the team's analysis is a series of vividly detailed, computer-simulated images illustrating the dark matter's location. According to the researchers, these images provide them with an unprecedented opportunity to infer dark matter's properties.

"The images we took show clearly that the cluster galaxies are located at the densest regions of the dark matter haloes, which are rendered in purple in our images," Jee said.

The work supports the theory that dark matter, which constitutes 90 percent of matter in the universe, and visible matter should coalesce at the same places because gravity pulls them together, according to the researchers.

Concentrations of dark matter should attract visible matter, and as a result, assist in the formation of luminous stars, galaxies and galaxy clusters, they said.

The clumped structure of dark matter is also consistent with the current hypothesis that dark matter particles are "collision- less," which means they do not collide and scatter like billiard balls but rather simply pass through each other.

"Collision-less" particles do not bombard one another as two hydrogen atoms do. If dark matter particles were collisional, a much smoother distribution should be yielded without any small- scale clumpy structures, they explained.

Dark matter presents a most challenging problem in cosmology. While its effects can be undoubtedly felt, its exact characteristics remain elusive because it is invisible.

Previous attempts to map dark matter in detail with ground- based telescopes were handicapped by turbulence in the Earth's atmosphere, which blurred the resulting images.

"Observing through the atmosphere is like trying to see the details of a picture at the bottom of a swimming pool full of waves, " said Holland Ford, a professor at the Johns Hopkins University and principal investigator of the work.

The team was able to overcome the atmospheric obstacle with the help of space-based Hubble telescope, whose sharpness and sensitivity of the images made it ideal for this project.

Source: Xinhua