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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.
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.
January 12, 2000