Lumpy local universe unveils cold message.

Lumpy local universe unveils cold message

A new map showing the distribution of galaxies across the sky has deepened the mystery of how galaxies formed after the Big Bang. Based on data from the Infrared Astronomical Satellite (IRAS), the map reveals that galaxies within 450 million light-years of the Milky Way have a markedly uneven arrangement. This heightens suspicions that the standard cold-dark-matter model of galaxy formation cannot adequately account for the huge galactic clusters and vast, intervening voids evident in the sky.

"There is more structure on large scales than is predicted by the standard cold-dark-matter theory," write Will Saunders of the University of Oxford in England and his collaborators in the Jan. 3 NATURE. To analyze the IRAS data, the team formulated a new statistical technique for measuring the degree of clustering in the three-dimensional distribution of matter on large scales.

"In the last two years, there have been lots of challenges to the cold-dark-matter model," says Lawrence M. Krauss of Yale University in New Haven, Conn. "this is the clearest statistical test [of the model] yet."

Although the results of the sky survey appear to rule out the simplest version of the cold-dark-matter scenario, in which the force of gravity acts on tiny fluctuations in the density of primordial matter to create galaxies, more complicated versions of the theory may still work. Indeed, Saunders and his co-workers furnish strong evidence that the universe must contain huge quantities of dark matter.

"It suggests that the way galaxies formed out of cold dark matter involved more complex processes than we had assumed," Krauss says. "As of now, there is no model that explains why the universe should be the way it is. Until now, cold dark matter provided the best possible model that was consistent with all the observations. It remains the best model that we have."

The new findings don't directly challenge the Big Bang scenario itself. "The Big Bang is in better shape than ever," says David N. Schramm of the University of Chicago. "What we don't know is how to make galaxies."