Hopkins Astronomers to Lead Search for Structure of Universe By Emil Venere A new telescope aimed at answering one of the most fundamental questions in cosmology is being developed by scientists at Hopkins and beyond. Now the quest for discovering the structure of the universe has received a financial boost. The National Science Foundation last month awarded a $5 million grant to the Sloan Digital Sky Survey, which involves scientists from Hopkins and other institutions in the United States and Japan. "The Sloan project is arguably the most exciting of the currently planned long-term projects in ground-based astronomy," said Alexander Szalay, a Hopkins professor of physics and astronomy who leads the team of scientists working on software for the project. "About two or three months into the project we will have more data than all astronomy had before." The survey, which is expected to take about five years to complete, will dramatically increase knowledge about galaxies. The best sky surveys now contain 2 million galaxies, but astronomers have reliable distance measurements for as few as 20,000 galaxies. The observatory, under construction in south-central New Mexico, may enable astronomers to survey 100 million galaxies and stars, some as far as 3 billion light-years away. Then, astronomers plan to concentrate on the brightest 1 million galaxies, studying details about their distance, age and composition, Dr. Szalay said. Hopkins scientists will design and build the telescope's spectrograph, an instrument that will enable astronomers to study about 100,000 quasars, or quasi-stellar radio sources, distant objects that look like stars when viewed through conventional telescopes but are actually hundreds of times brighter than an entire galaxy. "The idea is that we are going to pick up a lot of quasars in the process, which will give us another view of the structure of the universe," said Hopkins research scientist Alan Uomoto, project scientist for the team that is designing and building the spectrograph. "This is the first time that a large group of ground-based astronomers has gotten together to solve a particular research problem, and not just build a large instrument for general use." The challenge is determining the large-scale structure of the universe. By mapping the cosmos in detail, astronomers will learn how galaxies are organized into clusters and "superclusters," which ultimately will help cosmologists understand more about the processes leading to the present structure of the universe. Construction on the observatory began in the summer of 1993, with initial funding of $8 million from the Alfred P. Sloan Foundation. Scientists expect to begin testing the telescope within a year and have it fully operational in about two years. It is located at Apache Point, near Sunspot, N.M. The telescope will be extremely sensitive to distant light because its focal plane will be lined with charge-coupled devices, light-sensor chips used in video cameras that enable scientists to capture an image accurately. The typical large telescope has one CCD in its focal plane, but the Sloan telescope will contain 54 of the devices, 30 in the focal plane. The survey will cover half of the northern sky--or a quarter of the total sky--since the other half is obscured by the bright, nearby plane of the Earth's galaxy. Another major part of the project will be to make the volumes of information available to scientists and nonscientists. Over five years researchers will collect up to 20 trillion bytes of data, or roughly enough information to fill 10 million floppy disks. Just one night of observations will provide enough information to fill a few thousand floppy disks, Dr. Szalay said. Most of the sky survey information will be placed in a digital archive, probably in the form of compact discs, which will be made available to the public. It will be the first extensive collection of astronomical data recorded originally on computer. Many other sets of data in existing archives have been converted from original photographs into digital form for computer storage, reducing the clarity of the images. Researchers from the Physics and Astron-omy Department and the Computer Science Department are creating the archive software. The project is being managed by the nonprofit Astrophysical Research Consortium, whose members include Hopkins and several other institutions involved in the survey: Princeton University, the Institute for Advanced Study, the University of Chicago and the University of Washington. Also involved in the project are Fermi National Accelerator Laboratory, the Naval Research Observatory and a group of Japanese astronomers.
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