National Radio Astronomy Observatory
P.O. Box O
Socorro, New Mexico 87801
http://www.nrao.edu
NRAO Background Information
Contact:
Dave Finley, Public Information Officer
(505) 835-7302
dfinley@nrao.edu
The Very Long Baseline Array (VLBA)
A continent-wide radio telescope system
offering the greatest resolving power of any astronomical
instrument operational today
Overview: The National Science Foundation's VLBA is a system of ten
identical radio-telescope antennas controlled from a common
headquarters and working together as a single instrument. The radio
signals received by each individual antenna contribute part of the
information used to produce images of celestial objects with hundreds
of times more detail than Hubble Space Telescope images.
Scientific Areas: The VLBA can contribute to any astronomical
research area where quality, high-resolution radio images will advance
knowledge of the field. In its first five years of full operation, the
VLBA has produced dramatic new information in these areas:
- Stars: With the VLBA, astronomers have tracked gas motions in the
atmosphere of a star other than the Sun for the first time; made the
first maps of the magnetic field of a star other than the Sun; and
studied the violent dances of double-star pairs in which one of the
pair is a superdense neutron star or a black hole.
- Protostars, star formation, and protoplanetary disks: The VLBA has
provided scientists with some of the best views yet of very young stars
and the complex regions in which they are born. VLBA images have shown
outflows of gas from young stars and disks of material orbiting these
new stars -- material that later may form planetary systems.
- Supernovae and Supernova Remnants: The VLBA has directly
measured the expansion of a shell of exploded debris from the supernova
SN 1993J, in the galaxy M81, some 11 million light-years from Earth. This has
allowed scientists to learn new details about the explosion itself and
its surroundings as well as calculate the distance to the supernova by
using the VLBA data in conjunction with information from optical
telescopes. VLBA images have shown regions of shocked gas in supernova
remnants.
- The Milky Way: Radio waves from extragalactic objects, such as
quasars, are affected by variations in the interstellar medium of the Milky
Way. By measuring these effects with the VLBA, scientists are gaining
valuable information about this tenuous component of our own Galaxy.
Similar studies can tell about the distribution of hydrogen gas in our
Galaxy. The great resolving power of the VLBA will allow astronomers to
directly measure the distance to the Milky Way's center, some 30,000
light-years away, and has detected the tiny apparent shift in its
position caused by our Solar System's motion around that center. The
Solar System takes more than 200 million years to complete an orbit of
the Galaxy's center, but the VLBA can detect that motion in less than a
month!
- Other Galaxies and Active Galactic Nuclei: The sharp radio
"vision" of the VLBA has allowed scientists to study other galaxies in
unprecedented detail. Numerous VLBA studies have focused on active
galactic nuclei -- the "monsters" at the hearts of many galaxies
thought to harbor supermassive black holes at their cores. The black
hole is thought to be surrounded by a rotating disk of material being
sucked into it, and jets of subatomic particles accelerated to nearly
the speed of light by the gravitational energy of the black hole. VLBA
studies have given strong support to this "standard model" of an active
galactic nucleus, showing the accretion disk in several such systems,
and even measuring motions in one such disk. VLBA observations also
have provided strong evidence that the material in the jets may be a
mixture of matter and antimatter.
- Cosmology: The VLBA's resolving power has allowed the farthest
direct distance measurements yet made, of galaxies up to 23 million light-
years away. Farther still, the VLBA is being used to study
gravitational lenses in attempts to use such lens systems to accurately
measure extremely great distances, and thus to refine estimates of the
size and age of the universe. VLBA observations also are being used to
detect possible structure in extremely distant objects, to learn about
the nature of the universe when it was but a fraction of its current
age.
Operations: The VLBA is operated from the National Radio Astronomy
Observatory's (NRAO) Array Operations Center (AOC) in Socorro, New
Mexico. The staff of the AOC also supports the Very Large Array, a
system of 27 antennas 50 miles west of Socorro. The NRAO is a facility
of the National Science Foundation, and its instruments, including the
VLBA, are available to the scientific community on a peer-reviewed
basis. Scientists whose observing proposals are successful can obtain
extensive assistance from NRAO astronomers and technical staff in
preparing for their observations and in processing their data after the
observations. Through this process, numerous graduate students now are
using the VLBA for their dissertation research.
History: Construction of the VLBA began in 1986, and the
last observing station was completed in 1993. Astronomical observations
with the partially-completed system began in 1987. All 10 VLBA stations were
used for observing the first time in May of 1993. The official opening
of the VLBA was held in Socorro, NM, on August 20, 1993. The total cost
of constructing the VLBA was $85 million.
Stations: The VLBA has stations at: St. Croix, U.S. Virgin
Islands; Hancock, New Hampshire; North Liberty, Iowa; Fort Davis,
Texas; Los Alamos, New Mexico; Pie Town, New Mexico; Kitt Peak,
Arizona; Owens Valley, California; Brewster, Washington; and
Mauna Kea, Hawaii.
Technical Data: The VLBA's 240-ton dish antennas are 25 meters (82
feet) in diameter. They are equipped with receivers capable of
detecting signals at frequencies ranging from 300 MegaHertz to 86
GigaHertz in non-continuous bands. During observations, data is
collected at each station and recorded on magnetic tape. Each
18,000-foot reel of this tape holds 750 GBytes of data. Following
observation, the tapes are shipped to Socorro. In Socorro, the
VLBA Correlator, a special-purpose digital machine that combines
the signals from all antennas, can perform 750 billion
mathematical operations per second. The VLBA can produce images
with a resolution of less than a thousandth of a second of arc.
Such resolution is the equivalent of being able to stand in New
York and read a newspaper in Los Angeles. The VLBA routinely works
with other radio telescopes elsewhere in the world and in space.