Image Credit: NASA/STScI
Globs In Space
by Roland Pease
Princeton - August 23, 2000 - Could bizarre giant particles nearly as big as galaxies, but lighter than electrons, dig cosmology out of a hole? Physicists suggest the universe is jam-packed with these strange particles, which might explain why small galaxies are far rarer in the universe than theory predicts.

"I know it sounds crazy," says team member Andrei Gruzinov of the Institute for Advanced Study in Princeton, New Jersey. "But so far as we can tell, no observations rule it out."

The weird particles could solve a problem related to galaxy formation. Observations suggest galaxies formed when the universe was less than a billion years old as matter clumped together under gravity.

But astronomers have trouble explaining how they formed so early on. The normal matter that makes up galaxies and stars should have taken much longer to collapse into lumps.

To resolve this, they've suggested the universe contains lots of so-called cold dark matter, which is different from ordinary matter and clumps together more readily under gravity.

Shortly after the big bang, the cold dark matter would have collapsed into pools whose gravity subsequently dragged in the ordinary matter that builds galaxies, speeding up their formation.

But computer simulations since 1996 predict the cold dark matter should have continued to collapse under its own weight, forming dense nuggets not just at the cores of big galaxies, but at random points in space as well. These nuggets should also have attracted normal matter, forming huge numbers of dwarf galaxies--far more than we can actually see.

Now a team led by Wayne Hu of the Princeton Institute for Advanced Study has come up with an extraordinary solution to this predicament from the quantum world.

According to quantum theory, matter can behave as both particles and waves. Normally we don't see the wavelike characteristics of matter because their wavelengths are so small--usually atom-sized.

But Hu's team says that if a particle was light enough--just 10-24 times as heavy as an electron--its wavelength would be a massive 3000 light years. In other words, each particle's size would be a significant fraction of the size of a whole galaxy.

So a collection of these giant particles would not collapse into small nuggets, explaining the dearth of dwarf galaxies. Instead, these particles would form giant globs of "fuzzy" cold dark matter.

David Spergel, an astrophysicist at Princeton University, calls it a cute idea. But he adds that to avoid upsetting everything else we know, fuzzy matter could only feel one force--gravity--and that it would be almost impossible to detect.

Hu argues that looking at the shapes of dwarf galaxies could help reveal whether fuzzy matter really does exist. Although the idea is speculative, adds Gruzinov, it sets up a challenge to their peers: "Can you prove this wrong?"

Source: Physical Review Letters (vol 85, p 1158)

This article appeared in the August 26 issue of New Scientist New Scientist. Copyright 2000 - All rights reserved. The material on this page is provided by New Scientist and may not be published, broadcast, rewritten or redistributed without written authorization from New Scientist.

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