An effort to understand dark matter

Jan 10, 2007 12:36 GMT  ·  By

Astronomers hope to solve many mysteries surrounding the dark matter that scaffolds the stars and galaxies as a new three-dimensional map of this was been made. Till now, dark matter is known only as an invisible form of matter that does not reflect light yet compasses for the vast majority of mass in the universe. But "without dark matter as we are seeing here, the universe wouldn't exist as it is today," said Richard Massey, an astronomer at the California Institute of Technology (Caltech) in Pasadena.

The dark matter holds the universe together as it expands after the Big Bang, besides being a framework for the assembly of normal matter. "For the first time we have been able to map out the large-scale distribution of this invisible, mysterious dark matter," Massey said.

The imaging, part of the COSMOS (Cosmic Evolution Survey) project, is the result of a thousand hours of observations of 575 overlapping patches of sky with the Hubble Space Telescope's high-resolution cameras and ground telescopes in Hawaii and Chile. "It's the largest project that's ever been done by the space telescope," noted Caltech team member Nick Scoville.

The three-dimensional mass map depicts the shapes of about a half million faraway galaxies, whose light reached Earth traveling through dark matter. "While the researchers cannot see galactic light undistorted, statistical analyses of hundreds of galaxies allow the scientists to predict how the galaxies should look in the absence of dark matter," Massey explained.

The scientists inferred dark matter's distribution by the way the galactic light bent. The map presents dark matter strung out in a network of filaments that expand over time; they intersect in massive structures at the location of galaxy clusters, enhancing the idea that galaxies emerged along the densest concentrations of dark matter.

The researchers could also depict how dark matter has expanded increasingly clumpy as it has collapsed under gravity. Dark energy is a repulsive force opposing gravity, believed to bias the way dark matter clumps together. "This growth of these [dark matter] structures is a competition between the attractive force of gravity and the repulsive force, or almost an antigravity, of the dark energy," said Jason Rhodes, a study collaborator from the Jet Propulsion Laboratory in Pasadena.

"Follow-up missions will use the same gravitational lensing technique as the COSMOS mission to determine the nature of dark energy", added Rhodes.

"We haven't got an answer of what is dark matter yet. We got the first step though-that is, where is the dark matter", said Massey.