Researchers Shed Light on Dark Matter

"Dark matter" in the universe is far more structurally complex than previously imagined, according to a new computational model devised by UC Berkeley scientists.

The finding may lead to greater insights into the history of the early universe, as well as improved theories about fundamental astrophysical phenomena throughout the cosmos.

To understand the concept of dark matter, first consider that there is much more to the starry corridors of space than initially meets the eye.

"The currently favored cosmological model tells us that the universe is made of mainly two dark components-dark matter and dark energy," said UC Berkeley astronomy professor Chung-Pei Ma.

Dark matter and dark energy together account for nearly 99 percent of the mass of the universe, Ma said.

The stars, planets and other visible objects in the night sky compose the remaining, tiny percentage.

Though dark matter is essentially invisible, its role in the universe can be inferred from its interactions with "normal" matter through the force of gravity.

"We do know quite a few things about dark matter," Ma said. "Basically every galaxy is surrounded by a bigger halo of dark matter."

Previous computational models used to describe dark matter simulated a patch of the universe hundreds of millions of light-years across in width.

These models predicted dark matter formed smooth halos around galaxies.

Using simulated units of about a million solar masses in magnitude-quite small compared to previous models-Ma and others were able to increase the resolution, modeling the fine substructure of dark matter.

Contrary to the previous "smooth halo" model, these simulations showed that each parent halo is in fact surrounded by thousands of little satellite clumps of dark matter.

Interestingly, Ma and her collaborator Ed Bertschinger at MIT found that the effects of these "mini-galaxies" on the parent halo could be modeled by a mathematical equation similar to the one for Brownian motion, a 90-year-old classic theory that describes the seemingly erratic movement of particles caused by molecules in a liquid.

This work will soon be submitted for publication in The Astrophysical Journal.

Reproduction of the results with different computers, parameters and programs solidified Ma's belief in the validity of her model.

Ma hoped to pursue the implications of her theory, exploring the differential equation that she wrote down for the motion of dark matter in her little universe.

"We've just derived the equation," Ma said. "This was the hard part and has taken us more than a year. Solving it will tell us how dark matter moves and clusters in the young universe."

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