Hubble makes 3D dark matter map
Date: Sunday, January 07, 2007 @ 15:04:51 GMT
Topic: Science

By Paul Rincon
Science reporter, BBC News, Seattle

Astronomers have mapped the cosmic "scaffold" of dark matter upon which stars and galaxies are assembled.

Dark matter does not reflect or emit detectable light, yet it accounts for most of the mass in the Universe.

The study, published in Nature journal, provides the best evidence yet that the distribution of galaxies follows the distribution of dark matter.

This is because dark matter attracts "ordinary" matter through its gravitational pull.

Scientists presented details of their research during a news conference here at the 209th meeting of the American Astronomical Society (AAS) in Seattle, Washington.

It involved nearly 1,000 hours of observations with the Hubble Space Telescope.

According to one researcher, the findings provide "beautiful confirmation" of standard theories to explain how structures in the Universe evolved over billions of years.

Ordinary matter - gas, stars, planets and galaxies - makes up just one-sixth of all matter in the Universe. The remainder is unseen.

While previous studies of dark matter relied on simulations, this one details its large-scale distribution in 3D.

For astronomers, the challenge of mapping the Universe has been described as similar to mapping a city from night-time aerial snapshots showing only street lights.

Dark matter is invisible, so only the luminous galaxies can be seen directly. The new images are equivalent to seeing a city, its suburbs and country roads in daylight for the first time.

Yet puzzling discrepancies remain.

Light bending

The map of mass distribution is based on measurements of about half a million distant galaxies.

Lead author Richard Massey and his colleagues used a technique called weak gravitational lensing to detect the dark matter.

To reach us, the light from galaxies has to pass through intervening dark matter.

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