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New Pictures Reveal 100,000 Galaxies
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
13 August 2002
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In one of the strongest visible manifestations of the growing practice of "virtual observatories," the ESO has released a host of images -- some old, some new -- for astronomers to use as the basis for research
Billed by astronomers as a "joyride to infinity," a photograph of a relatively small patch of sky in the Southern Hemisphere peers through a galaxy to reveal more than 100,000 distant galaxies.
The picture, anchored by a stunning spiral galaxy called NGC 300 that is front and center, was taken with the European Southern Observatory's 2.2-meter (7.2-foot) telescope at the La Silla Observatory in Chile. Created with archived data, the image was released to the public last week. The raw data behind it is available to astronomers for new discoveries as part of an online "virtual observatory" program. The remarkable array of galaxies is only revealed in close-ups of the picture, which also show countless foreground stars associated with NGC 300. While NGC 300 is just 7 million light-years away, the mean distance of the background galaxies is 8 billion light-years. able -->  | | SCIENCE TUESDAY | | | | | |  |  | Images |
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 | Located 7 million light-years away in the Southern Hemisphere constellation Sculptor, this spiral galaxy called NGC 300 is similar to our Milky Way. In the background of the image are 100,000 galaxies, fully revealed only in more detailed versions of the photo.
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| In this close-up of the new photo, some of the 100,000 more distant galaxies can be seen as one peers through the stars on the outskirts of the galaxy NGC 300.
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| | |  | TODAY'S DISCUSSION | | | | | | | Mischa Schirmer, an astronomer at the University of Bonn, produced the photograph from data that was gathered in 1999 and 2000 by Wolfgang Gieren and his colleagues in Chile for a different research project. "A single image showing 100,000 galaxies is indeed a little unusual," Schirmer told SPACE.com. "In order to achieve it, one needs very long exposure times, good atmospheric conditions and a wide field of view." The La Silla telescope fits the wide-field bill, seeing an area of the sky roughly equal to the size of the full Moon. Most other high-powered telescopes typically image much smaller patches of sky. Upwards 30 hours of cumulative exposure time was required to generate the picture. The raw data occupies 150 gigabytes of computer disk space. In high-resolution versions of the photograph to be released soon on CD-ROM, interesting relationships between galaxies emerge. "It becomes clear that galaxies are distributed in a highly non-uniform way," Schirmer said. "Probing this non-uniformity helps in understanding the evolution of structure in the universe." He added, however, that other, similar images from different parts of the sky are needed to draw overall conclusions. Yet this sort of wide-field imaging on a grand scale of very distant objects is a young and highly demanding sector of observational astronomy, he said. Schirmer said the photograph is also interesting because it happens to reveal a cluster of galaxies. Employing certain techniques, astronomers can measure the amount of so-called dark matter in the cluster. Dark matter is stuff that can't be seen but which astronomers presume to exist because of the mere fact that individual galaxies don't fly apart and also because of the gravitationally bound conglomerations of galaxies they find throughout the universe. "There is about 10 times more dark matter than 'normal' matter in the universe," Schirmer said. "Its nature is still unclear." The new photo also reveals three highly active galaxies called quasars. These distant objects are widely supposed by astronomers to be galaxies anchored by supermassive black holes that each contain the mass of millions or even billions of stars. As a black hole consumes huge quantities of gas, the material becomes superheated while it spirals inward and approaches the speed of light. The process generates tremendous amounts of X-rays, light and other radiation that makes a quasar stand out in a crowd, since they can appear thousands of times brighter than galaxies that do not contain active black holes. "Such deep images help in studying the environment of those quasars [and examining] how their strong output of radiation influences the evolution of its neighboring galaxies," Schirmer said. The exposures from which the color composite of NGC 300 was created are part of the searchable ESO Science Data Archive an online database designed to serve astronomers with various sorts of observations made using ESO telescopes. [see related image gallery near the top-right of this page], Such so-called virtual observatories are thought by many astronomers to have a promising future because actual observing time is highly competitive and because various research institutions have racked up many terabytes of useful data, from ground- and space-based observatories, that have yet to be mined.More Deep Space News | Astronotes
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