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. Arecibo Survey Produces Dark Galaxy Candidate

Arecibo's AGES galactic survey found 10 radio sources in this image, including dark-galaxy candidate NGC 1156 (lower left) and four galaxies moving between 10,000 and 11,000 kilometers (6,820 miles) per second. Image credit: NAIC/AGES
by Staff Writers
Leicester England (SPX) Apr 07, 2006
Results from the Arecibo Radio Telescope's new Galaxy Environment Survey show what appears to be the first candidates for mysterious objects called dark galaxies, which burn brilliantly in radio wavelengths but are almost invisible to optical telescopes. Dark galaxies could help explain where part of the so-called missing mass of the universe is hiding.

The AGES survey, begun last January, is the most sensitive, large-scale survey of neutral hydrogen to date. Neutral hydrogen is found in most galaxies and is considered a key tool in the search for dark galaxies, because it can be detected even when there are no stars or other radiation sources shining.

AGES has found a possible dark galaxy near NGC 1156, an apparently isolated, irregularly-shaped galaxy found at the edge of the constellation Aries - also known as The Ram. The survey also has identified several other possible dark galaxies, including one about 150-million light-years away that appears to be 200,000 light-years across - double the size of the Milky Way. Astronomers know of no optical counterpart to the massive object.

"The new source showed up clearly in the AGES survey, as it contains huge amounts of hydrogen gas, but it was missed in all previous searches, as it doesn't appear to contain many bright stars," said team member Robbie Auld of Cardiff University in Wales. "The interactions between hydrogen atoms in cosmic gas clouds are enough to stimulate light emission at the neutral hydrogen fingerprint wavelength of 21 centimeters."

Reporting at a meeting of the Royal Astronomical Society, Auld said the AGES team used the Arecibo radio telescope to search the neutral-hydrogen wavelength for galaxies that have remained hidden from astronomers in the past. "We now need to follow up observations at other wavelengths and work out exactly how many stars this new galaxy may or may not contain," he said.

The same survey techniques used by AGES, but on a smaller scale, have led to the discovery of VIRGOHI21, the first galaxy known to contain gas and large amounts of dark matter, but no visible stars. By locating more objects like VIRGOHI21, astronomers hope to answer one of the great cosmological questions: If, as theoreticians predict, matter in the universe is mainly dark, then where does is all reside? The AGES team hopes the survey will reveal exactly how much matter is hidden in dark galaxies, which could help to verify current theories.

AGES is a collaboration of two-dozen institutions, including 13 universities and 11 observatories. It will last for four years and is led by Jonathan Davies of Cariff University. In addition to the Arecibo radio telescope, AGES uses a network of ground-based and space-based telescopes to observe the sky in many different wavelengths, including U.K. Infrared Telescope in Hawaii, the GALEX ultraviolet space telescope and the Hubble Space Telescope.

Related Links
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Spitzer Sees New Planet Disk Around Dead Star
Pasadena CA (SPX) Apr 07, 2006
NASA's Spitzer Space Telescope has uncovered new evidence that new planets could emerge from the ashes of a supernova around dense, rapidly spinning stellar remnants called pulsars. "Now we can say that (planets around pulsars) are not uncommon," Aleksander Wolszczan of Penn State University told reporters at a news briefing about the discovery.

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