International Space VLBI Mission Yields Most Detailed Views Of Quasars
Ron Baalke
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Michelle Viotti (818) 354-8774
FOR IMMEDIATE RELEASE January 12, 2000
INTERNATIONAL SPACE VLBI MISSION YIELDS MOST DETAILED VIEWS OF QUASARS
Astronomers from around the world will gather in Japan later this
month to present the most detailed images of quasars ever seen, produced
with data from the Very Long Base Interferometry Space Observatory Program.
Space VLBI, as this is known, is a new type of astronomy mission that uses a
combination of satellite- and Earth-based radio antennas to create a
telescope more than two-and-a-half times the diameter of the Earth.
As the largest astronomical instrument ever built, Space VLBI has
given astronomers one of their sharpest views yet of the universe.
Astronomers plan to present a number of stunning new radio images in
a January 19-21 symposium at Japan's Institute of Space and Astronautical
Science (ISAS) near Tokyo. Many of these images depict quasars whose radio
emission has traveled billions of light years to reach Earth.
"These images probe some of the most distant, ancient, and energetic
objects in the universe, giving us a glimpse of quasars as they existed
billions of years ago," said Dr. Robert Preston, U.S. Space VLBI project
scientist at NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif. "These
powerful objects exist at the center of many galaxies, including our own
familiar Milky Way, which contains a very weak version of a quasar."
Launched in February, 1997 by Japan's ISAS, Space VLBI uses a
technique called interferometry that electronically links widely separated
telescopes so that they work together as a single instrument with
extraordinarily sharp "vision" or resolving power. By taking this technique
into space for the first time, astronomers have approximately tripled the
resolving power previously available with only ground-based telescopes. "The
Space VLBI satellite system has more than 100 times greater resolving power
in radio frequencies than the Hubble Space Telescope has at optical
wavelengths." said Preston. "In fact, its resolving power is equivalent to
being able to read a newspaper headline in Tokyo all the way from Los
Angeles."
Quasars are enormously bright point-like optical objects, often
shining with an intensity many hundreds of times brighter than that of an
entire galaxy. However, they are so distant that they appear only as very
faint points of light to optical telescopes on Earth. Scientists believe
that quasars are powered by gases such as remnants of stars spiraling into
black holes at the centers of galaxies. Black holes are so massive that no
light or matter can escape from their immensely strong gravity and, in the
case of quasars, they can have masses that are millions to billions of times
that of our own sun. Although most in-rushing matter is captured forever by
the black hole, some of the material is likely ejected at enormous speeds to
form the observed narrow radio-emitting jets. By studying these jets, which
are usually visible only at radio frequencies, astronomers hope to learn
more about the black holes that power them.
Key results from Space VLBI include clearly resolved individual
components in the observed quasars' jets. Perhaps the most significant
single result of the Space VLBI mission so far is the detection of a number
of radio sources associated with quasars that are intrinsically brighter
than theory generally allows for a stationary source. However, a bizarre
prediction of Einstein's theory of relativity is that radiation from an
object moving at near light speed will be beamed in the direction of motion.
Therefore, rather than looking equally bright from all directions (like a
light bulb), the source looks much brighter if it is moving rapidly toward
us (like looking into the beam of a flashlight). This effect allows some
sources to appear much brighter than they really are, solving the conflict
between the observed and theoretically allowed brightness of the radio-
emitting quasars. As a consequence, the recent observations imply that the
radio-emitting plasma in these sources is actually moving toward us at
nearly the speed of light in accordance with Einstein's prediction. While
astronomers had suspected this outcome for many small, bright, radio
sources, Space VLBI observations help prove that this idea is correct.
Fine details revealed by Space VLBI images have also been combined
with observations of the same objects in other parts of the spectrum (such
as infrared, optical, ultraviolet, X-ray, and gamma ray). For example, the
recently launched Chandra X-ray telescope detected bright X-ray emission
from the core of a distant quasar named PKS 0637-752, as well as a very
unexpected source of X-ray emission coming from part of the quasar's radio
jet. Space VLBI observations show the intricate radio structure in the core
of this quasar with a thousand times finer detail, and measure the speed of
material in the radio jet by comparing images made at different times.
Knowing the speed of the jet allows astronomers to define better the
physical processes responsible for generating the X-ray emission.
Not all space VLBI observations have been of very distant objects.
Space VLBI observations have also helped determine the size and shape of an
extremely bright radio source in a nearby star-forming region of the
constellation Orion. These observations indicate that the intense,
narrow-band, radio emission from water molecules in the star-forming region
comes from areas with strong magnetic fields.
The new radio images and related images are available at
http://www.jpl.nasa.gov/pictures/spacevlbi/ . Additional information about
the U.S. Space VLBI mission is available at
http://us-space-vlbi.jpl.nasa.gov/ .
Space VLBI is part of a major international undertaking. Led by
Japan's ISAS, the VLBI Space Observatory Program enables about 40
Earth-based radio telescopes from more than 15 countries to co-observe with
the space VLBI satellite. The network spans the globe, in the northern
hemisphere from the United States to Europe to Asia, and in the southern
hemisphere from eastern Australia to South Africa. More than 70 scientists
associated with collaborating institutions are expected to attend the
conference at ISAS.
NASA's Jet Propulsion Laboratory, Pasadena, CA, a division of the
California Institute of Technology, manages the U.S. portion of the Space
VLBI international consortium on behalf of NASA's Office of Space Science,
Washington, D.C.
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