On Research: Astronomers Peer Deep In Space, Far Back In Time Hubble Sheds Light On Small, Odd-Shaped Galaxies Emil Venere ----------------------------------- Homewood News and Information A team of astronomers has used the Hubble Space Telescope to solve a 20-year mystery: what is the nature of an enormous number of faint galaxies seen by the world's largest telescopes in the deepest regions of the universe? After a year and a half of using the repaired space telescope, scientists have learned that the blue-colored objects are actually small, odd-shaped galaxies that become more numerous as astronomers look deeper into space, and therefore farther back in time. But in the process of learning more, astronomers have raised new questions. The faint galaxies are seen everywhere in the sky; astronomers using ultra-powerful telescopes see tens of thousands of them in an area the size of the full moon. Some of the galaxies are as distant as six billion light-years away. They emit blue light because they are in the process of hatching many new stars at once, stars that are massive and very hot, said Richard Griffiths, who heads an international project called the Medium Deep Survey, which uses the Hubble Space Telescope. Astronomers aren't sure where all the faint galaxies are today. They may still be just as numerous as they were billions of years ago but are not as bright as they used to be, making them more difficult to see, said Griffiths, an associate research professor in the Department of Physics and Astronomy. The survey's main goal was to learn the nature of the distant objects. "We've come a long way in terms of solving that particular problem," Griffiths said. Scientists on the survey team are using the space telescope's Wide Field Planetary Camera-2, which was part of a package of corrective optics installed in December 1993, during a mission to repair an image-blurring mirror flaw. Griffiths was a member of the team of scientists responsible for building the new camera. Shortly after the orbiting observatory was launched, in April 1990, it was discovered that the telescope's primary mirror was not ground to the proper shape. Much of the original wide field planetary camera's function was negated by the mirror's flaw, since it prevented the telescope from focusing light into a tight point, resulting in fuzzy halos around images. That made it very difficult, if not impossible, to pick out faint objects in a field of brighter objects. Although astronomers can see faint galaxies with the largest telescopes on Earth, even the most powerful ground-based telescopes cannot resolve details. Astronomers had to wait until the space telescope's blurry vision was corrected before they could get a good look at the galaxies. "We've known about them for nearly two decades, but we didn't know what they were," Griffiths said. "We couldn't say anything about their actual structure." Scientists have learned that the galaxies are about one-tenth the size of the typical elliptical and spiral galaxies, like our Milky Way, previously thought to dominate the universe. Whereas galaxies common in today's cosmos might contain about a hundred thousand million stars, the very faint, distant galaxies contain roughly a thousand million stars, Griffiths said. Not only are they much smaller, they also have irregular shapes, unlike the nearly symmetric spiral and elliptical galaxies. Astronomers are puzzled about whether the small galaxies were the building blocks of large galaxies like the Milky Way, or whether they have simply faded into obscurity. While some of the odd-shaped galaxies might have merged to form large galaxies, it now appears more likely that many of them did not. "They are apparently not merging into big spirals because we don't see them around big spirals," Griffiths said. "We see them everywhere and they're mainly isolated objects, not in pairs or groups." That adds a new chapter to the mystery: where are the small galaxies today? Scientists think many of them may still exist but cannot be seen because they have grown much fainter over the years. If that's true, perhaps large telescopes on the ground might be used to find the galaxies, Griffiths said. "If you want to look at nearby galaxies of this kind you have to do very large area surveys," he said. The space telescope can take in only small areas of the sky at a time, an area about one-tenth the diameter of the moon. The latest findings made by a team of astronomers led by Griffiths will be published this month and in November in the Astrophysical Journal. One of their papers was published July 15 in Britain, in the Monthly Notices of the Royal Astronomical Society. Scientists based their findings directly on an extensive Medium Deep Survey database put together by astronomer Kavan Ratnatunga, an associate research scientist in the Hopkins Department of Physics and Astronomy, and his colleagues at Hopkins. However, the data are yielding many additional cosmic fruits, besides the faint galaxy findings. Although astronomers could not use the original wide field camera to study faint galaxies, the instrument could be used for other research. For example, the survey, which began in 1990, has enabled scientists to learn details about the frequency of exceptionally bright galactic cores, called active galactic nuclei. It also has provided insights into "gravitational lenses," the bending and shaping of light by massive objects. Astronomers have studied two such lenses; light from a faint blue galaxy or quasar located exactly behind the center of an elliptical galaxy is distorted as it passes through the center of the elliptical galaxy. As seen by viewers on Earth, the light is forced into the shape of a cross. Astronomers on the survey team have published about 30 scientific papers so far.
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