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1993-05-03
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PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. (818) 354-5011
FOR IMMEDIATE RELEASEJune 27, 1991
Astronomers studying very faint objects originally
detected by the Infrared Astronomical Satellite (IRAS) have
discovered a new, very distant object which they say is the most
luminous object ever seen in the universe.
The observations, published today (June 27) in the
British science journal Nature, show that the luminous object is
a massive dust cloud which radiates 99 percent of its light in
the infrared part of the spectrum.
The team of astronomers believe that this mysterious
cloud may be a massive galaxy in the process of formation -- or,
alternatively, a quasar embedded in the dust of a massive galaxy.
Infrared light -- or, more simply, heat radiation --
is invisible to the human eye, but can be detected by
electronic sensors such as those on the IRAS satellite.
IRAS discovered hundreds of thousands of infrared objects
that astronomers are now observing more closely in order to
determine what they are. Often these sources turn out to be
dusty objects, because dust particles are very efficient emitters
of infrared radiation.
Astronomers define the luminosity of an object as the
total amount of energy emitted at all wavelengths. The
luminosity of this newly found object is an incredible 300
trillion times that of the sun, or 30,000 times that of our
entire Milky Way Galaxy, which itself consists of hundreds of
billions of stars like the sun. This tremendous energy output is
greater even than the most luminous known quasars, which were
discovered in visible or ultraviolet light. Quasars are thought
to derive their immense power from the presence of massive black
holes in their centers.
Unlike typical quasars, this new source is emitting
most of its light in the infrared region of the spectrum of
light. The dust cloud which the team believe is responsible for
the far-infrared radiation has a mass of between 400 million and
1 billion times that of the sun. The lower figure exceeds the
mass of interstellar dust in any previously known galaxy. The
higher figure is comparable to the whole mass of heavy elements
in the Milky Way Galaxy, most of which is today locked up in
stars.
The object, in the constellation of Ursa Major, is
approximately 16 billion light-years from Earth. When
astronomers study distant objects they are essentially looking
back in time; in this case the object is seen as it was 16
billion years ago, or more than 80 percent of the way back in
time to when the universe is thought to have originated in the
Big Bang.
The team of astronomers, from four British universities
and two U.S. institutions, is led by Prof. Michael Rowan-Robinsonof Queen Mary and Westfield College, London.
The team first observed the mystery object as part of a
program to identify infrared sources detected by IRAS.
The luminous dust cloud was discovered when the team
was trying to locate a visible light counterpart for one of the
new faint IRAS sources (the luminous source appears faint due to
its tremendous distance from us) at the United Kingdom's 4.2-
meter (13.7-foot) William Herschel Telescope in the Canary
Islands. Using a spectrometer, they were able to detect the
signatures of elements such as carbon and hydrogen in the faint
mystery source.
The redshift -- or shift of the characteristic element
lines towards the red end of the spectrum caused by the expansion
of the universe -- is 2.236, showing the object to be a very
distant galaxy. (The universal expansion causes more distant
parts of the universe to appear to be receding from us more
rapidly; thus, the more distant the object, the larger the
measured redshift of the spectral lines.)
More detailed images and spectra were later obtained at
Caltech's 200-inch telescope at Palomar Observatory, near San
Diego, and the William Herschel Telescope.
A joint mission between the United States, Netherlands
and United Kingdom, IRAS was launched by NASA in 1983. For 10
months it surveyed the entire sky, providing our first ever
comprehensive view of the universe at four different infrared
wavelengths.
In 1985 the U.S. Infrared Processing and Analysis
Center (IPAC), funded by NASA and based at the Jet Propulsion
Laboratory and the California Institute of Technology, produced a
catalog of sources detected by IRAS. From 1985-1988 IPAC re-
analyzed the satellite data to produce a more sensitive catalog
of infrared sources.
The powerhouse that heats the massive dust cloud and
causes it to glow so brightly in infrared light is hidden from
view, but the astronomers theorize that it may be due to about a
billion extremely hot, luminous young stars formed in the early
stages of the birth of a galaxy. If their theory is correct,
this discovery marks the first time astronomers have witnessed
the birth of a galaxy.
An alternate theory is that the powerhouse is itself a
quasar, more luminous than ever seen before, shrouded from our
view by the cloud of dust. Astronomers from other observatories
around the world have begun to train their telescopes on the new
object to shed further light on how galaxies and quasars formed
during the early history of the universe.
Joining Rowan-Robinson on the team of astronomers
involved in the discovery are Dr. Tom Broadhurst, Dr. Andy
Lawrence, Seb Oliver and Andy Taylor of Queen Mary and Westfield
College, London; Dr. Richard McMahon of the Institute of
Astronomy, University of Cambridge, England; Dr. Carol Lonsdale,
Dr. Perry Hacking and Tim Conrow of the JPL/Caltech IPAC; Prof.
George Efstathiou and Dr. Will Saunders of the University ofOxford, England; Prof. Richard Ellis of the University of Durham,
England; and Dr. Jim Condon of the National Radio Astronomy
Observatory, Charlottesville, Virginia.
JPL contributions to the project, as well as the U.S.
portion of the IRAS mission, are funded by NASA's Office of Space
Science and Applications.
#####
6-27-91 MAH/FOD