Rutgers astronomer sheds new light on dark matter

December 11, 2001

NEW BRUNSWICK/PISCATAWAY, N.J. - Rutgers astronomy researcher Licia Verde, together with Dr. Alan Heavens of the University of Edinburgh, has led an international team of 30 scientists in shedding new light on dark matter - one of the great mysteries of the universe. They found this invisible and mysterious substance distributed in a pattern parallel to the arrangement of the galaxies, tracing them closely.

Refining its relationship to the galaxies also allowed them to assess its quantity.

Scientists from a dozen institutions in the United States, Britain and Australia used the largest-ever survey of more than 200,000 galaxies, made with the Anglo-Australian Telescope, in New South Wales, Australia. They analyzed in detail how the galaxies are clustered, relating their distribution to the gravitational pull of the dark matter.

"Where there is matter, there is gravity and its pull has 'clumped' the galaxies into an uneven distribution," said Verde, a postdoctoral researcher at Rutgers with a joint appointment to the Princeton University Observatory. "There is much more dark matter than there is mass in the galaxies, so the force it exerts has moved the galaxies around." She explained that, were it not for the dark matter and its gravitational forces, the galaxies would be in a much more uniform pattern.

Scientists would like to see where the dark matter mass is, but telescopes can only see light, from bright objects such as galaxies. Verde explained that it is like looking at a Christmas tree at night; you see only the lights, but not the whole tree. This had limited what researchers could learn from studying galaxy positions. With the application of new computer analyses and gravitational theory, the astronomers have now been able to work out where the dark matter is. It is just what is to be expected if galaxies and dark matter are clustered in exactly the same way.

Verde added, "Knowing how clustered the dark matter is, also reveals how much of it there is - about seven times as much as ordinary matter; but only a quarter of what is needed to slow down the expansion of the universe to a halt."

The findings are presented in a paper submitted to the Monthly Notices of the Royal Astronomical Society with Verde as its lead author. (The paper appears electronically at http://xxx.lanl.gov/abs/astro-ph/0112161).

A second study, led by Dr. Ofer Lahav of Cambridge University, contrasted the same galaxy distribution map to the distribution of temperature fluctuations in the cosmic microwave background radiation - a sea of microwaves that exists everywhere in the universe and represents an "echo" of the Big Bang. It is difficult to measure, but tiny fluctuations in its temperature can reveal the kinds of matter and energy that compose the universe.

"The second paper looks at the relationship of the galaxies to a totally different set of phenomena, but the scientists got the same result, independently confirming our findings," said Verde.
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Rutgers University

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