SETI [ASTRO] New Digital Sky Survey Uncovers Rare Celestial Objects

Larry Klaes (
Fri, 04 Jun 1999 17:59:16 -0400

>X-Authentication-Warning: majordom set sender to owner-astro using -f >Date: Fri, 4 Jun 1999 1:07:21 GMT >From: Ron Baalke <> >To: >Subject: [ASTRO] New Digital Sky Survey Uncovers Rare Celestial Objects >Sender: >Reply-To: Ron Baalke <> > >Media Relations >Caltech > >Contact: >George Djorgovski, (626) 395-4415, >Robert Tindol, (626) 395-3631, > >Embargoed for release at 9 a.m. CST, Monday, May 31, 1999 > >New Digital Sky Survey Uncovers Rare Celestial Objects > >CHICAGO -- A large new digital sky survey has been used by astronomers at >the California Institute of Technology to discover distant quasars and other >rare types of cosmic objects, including mysterious new objects of an unknown >nature. > >These results are being reported today at the meeting of the American >Astronomical Society in Chicago. > >The Caltech team, led by S. George Djorgovski, professor of astronomy, made >the discoveries in an initial scientific exploration of the Digital Palomar >Observatory Sky Survey (DPOSS). The survey, now nearing completion, covers >the entire northern sky in three colors, and it is based on a photographic sky >atlas (POSS-II) produced at Palomar Observatory. > >The final product of the survey is the Palomar-Norris Sky Catalog, which will >contain information on over 50 million galaxies and about two billion stars. >It will be made available to the general astronomical community, beginning a >few months from now. > >When complete, the digital survey (DPOSS) will contain several terabytes of >information (a terabyte is 8 trillion bits, or about the amount of information >contained in two million thick books). This is also over a thousand times >larger than the amount of information in the entire human genome. > >Comparable amounts of data are now being produced by several other digital >sky surveys, including the Two-Micron All-Sky Survey (2MASS) in the infrared >wavelengths, the forthcoming Sloan Digital Sky Survey (SDSS), which like >DPOSS will cover the visible light part of the spectrum, and several NASA >missions. Other projects of a similar scope are now under way or are being >planned. > >"This is the dawn of the new era of information-rich astronomy," says >Djorgovski. "This unprecedented amount of astronomical information will >enable scientists and students everywhere, without access to large telescopes, >to do first-rate observational astronomy." > >Surveys like DPOSS can be used to study the universe in a systematic manner -- >for example, to probe the large-scale structure in the distribution of galaxies >in some detail. But they can also be used to discover rare, or even previously >unknown types of astronomical objects: the sheer numbers of detected sources >make it possible to find objects that are one in a million or even one in a >billion -- an astronomer's needle in a digital haystack. > >Caltech astronomers did exactly that in their initial scientific verification >tests of the DPOSS data. The group used novel techniques to search the data >for star-like objects with colors unlike those of the ordinary stars. > >Some of these are types of objects they expected to find: for example, very >distant quasars, seen at the time when the universe was less than ten percent >of its present age. Such quasars are valuable probes of the early universe and >galaxy formation. The Caltech team has so far identified over 70 of them, >more than the number found by all other groups in the world combined. > >Perhaps even more interesting are surprises, unexpected findings of anomalous >objects. The Caltech team has one such object whose nature is still unknown. > >"It has a spectrum unlike anything else I have ever seen," says Djorgovski. >"We have combed the literature and asked all kinds of experts, but no one can >tell us what it is. It is the first one of something new -- and a complete >mystery to us." > >Another discovery is objects that can vary in brightness by a large factor. >Since the photographs used in DPOSS are taken at different times in different >filters, objects that are much brighter at one time would stand out as having >peculiar colors. One such discovery is a starlike object which is associated >with an extremely faint galaxy. > >When the survey photograph was taken, the object was several hundred times >brighter than the galaxy itself, perhaps a hundred times brighter than a >supernova explosion. Astronomers speculate that it may have been associated >with an undetected gamma-ray burst, but it could also be something even more >strange and previously unseen. > >Astronomers at Caltech and elsewhere are discussing the concept of the >future National (or Global) Virtual Observatory, to be built in cyberspace >rather than on some mountaintop. This would be a way to organize and >combine many of the large new and forthcoming sky surveys and other >astronomical data, to make them accessible over the Web, and to provide >novel data-mining tools for their scientific exploration. > >Astronomers and computer scientists are now starting collaborations to make >this vision a reality. This would be a new way of doing astronomy, with a >computer and a rich data archive, rather than with a telescope. > >"We are really only beginning to explore the universe in some detail. There >must be many wonderful new and unexpected things out there, waiting to be >discovered, and large sky surveys are the best way to find them," concludes >Djorgovski. > >In addition to Djorgovski, the Caltech team includes postdoctoral scholars >Stephen Odewahn and Robert Brunner, graduate student Roy Gal, and several >Caltech undergraduates. Professor of Physics Tom Prince is also one of the >leaders of the effort to create the Virtual Observatory. > >The work on the DPOSS survey is supported by a grant from the Norris >Foundation and by other private donors. > >Images of the peculiar objects are available at: > > >RELATED LINKS > >Caltech's Palomar Observatory > > >

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