Astronomers Baffled by Space Light
By MATTHEW FORDAHL, AP
06:58 PM ET 08/17/99
LOS ANGELES (AP) - A mysterious celestial object detected three years ago in the
northern sky is baffling scientists who have been unable to figure out its makeup or how
far it is from Earth. It's rare for astronomers to find an unexplainable object, but
it's even more unusual for it to remain undefined for more than a week, said S. George
Djorgovski, a California Institute of Technology astronomer who helped discover the
object. ``It's fairly uncommon to stumble on something you don't have a clue about,'' he
said Tuesday. ``It certainly hasn't happened to me, and I've been doing this for many
years.''
Djorgovski and his team at Caltech's Palomar Observatory detected the object, a
pinpoint of light, during a digital survey of the northern sky.
Usually, astronomers are able to determine an object's composition and distance
by breaking down its light into a spectrum and analyzing it.
But the mystery object's spectrum does not fit any of the known patterns.
Scientists are unsure whether the object is inside our Milky Way galaxy or at the edge of
the universe.
Repeated photographs revealed no changes in its appearance. That ruled out the
possibility that it's an exploding star or supernova. Some astronomers believe the
object may be a new class of quasar, sources of energy found in the center of galaxies and
believed to be powered by matter falling into massive black holes. Djorgovski challenged
fellow astronomers to help explain his discovery at the June meeting of the American
Astronomical Society in Chicago, but nobody has produced an adequate explanation. ``We
probably have looked at the spectra of several thousand quasars, and this just doesn't
seem to fit,'' said David Crampton, an astronomer with the National Research Council of
Canada. ``It didn't ring any bells.''
The next step will be to analyze the object's infrared spectrum, something
Djorgovski hopes to do next month at the Keck Observatory in Hawaii.
Researchers also hope that the Hubble Space Telescope might someday be pointed
at the object, which is located in the constellation Serpens.
The Digital Palomar Sky Survey, which has collected information on more than 50
million galaxies and about 2 billion stars, is about two-thirds complete. The DPSS and
other sweeping surveys like it are likely to create more mysteries.
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, 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 10 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 with 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.
Contact: George Djorgovski (626) 395-4415 george@oracle.caltech.edu
Robert Tindol (626) 395-3631 tindol@caltech.edu
Related Links:
Caltech's
Palomar Observatory
