Prototype for Long Wavelength Array Sees First Light (Forwarded)

Public Affairs Office
Naval Research Laboratory
Washington, D.C.

3/29/2007

NRL Press Release 15-07r

Prototype for Long Wavelength Array Sees First Light

Astronomers at the Naval Research Laboratory have produced the first images
of the sky from a prototype of the Long Wavelength Array (LWA), a
revolutionary new radio telescope to be constructed in southwestern New
Mexico. The images show emissions from the center of our Galaxy, a
supermassive black hole, and the remnant of a star that exploded in a
supernova over 300 years ago. Not only a milestone in the development of the
LWA, the images are also a first glimpse through a new window on the cosmos.
"First light" is an astronomical term for the first image produced with a
telescope. It is a key milestone for any telescope because it indicates that
all of the individual components are working in unison as planned.

Once completed, the LWA will provide an entirely novel view of the sky, in
the radio frequency range of 20-80 MHz, currently one of the most poorly
explored regions of the electromagnetic spectrum in astronomy. The LWA will
be able to make sensitive high-resolution images, and scan the sky rapidly
for new and transient sources of radio waves, which might represent the
explosion of distant, massive stars, the emissions from planets outside of
our own solar system or even previously unknown objects or phenomena.

"The LWA will allow us to make the sharpest images ever possible using very
long wavelength radio waves. This newly opened window on the universe will
help us understand the acceleration of relativistic particles in a variety
of extreme astrophysical environments including from the most distant
supermassive black holes. But perhaps most exciting is the promise of new
source classes waiting to be discovered," says Dr. Namir Kassim, an NRL
astronomer in the Remote Sensing Division and LWA Project Scientist. Dr.
Tracy Clarke, of Interferometrics, Inc. in Herndon, Virginia, another
astronomer on the NRL team adds, "By detecting distant clusters of galaxies
the LWA may also provide new insights on the cosmological evolution of the
mysterious dark matter and dark energy."

Although radio astronomy was discovered at low frequencies (near 20 MHz,
corresponding to wavelengths of 15 meters), well below the current FM band,
astronomers quickly moved up to higher frequencies (centimeter wavelengths)
in search of higher resolution and to escape the corrupting effects of the
Earth's ionosphere, a region of charged particles between about 50 and 600
miles above the surface. The ionosphere, which can "bend" radio waves to
produce long-distance reception of AM and short-wave radio signals, also
causes distortions in radio telescope images in much the same way that
atmospheric irregularities cause twinkling of stars. Ionospheric effects
become much worse at low frequencies, but new imaging techniques developed
at NRL and elsewhere have allowed the "ionospheric barrier" to be broken and
enabled high-resolution astronomical imaging at these low frequencies for
the first time.

These new imaging techniques provide an improved view of not only the
astronomical sky, but the Earth's ionosphere as well. The full LWA will
generate richly detailed measurements of the ionosphere that will complement
other ionospheric data sources. Understanding the ionosphere is critically
important to the Department of Defense because of its effects on
communications and navigation systems.

The current prototype, referred to as the Long Wavelength Demonstrator Array
(LWDA) to differentiate it from the larger LWA project, completed
installation on the Plains of San Agustin in southwestern New Mexico in the
fall of 2006. Funded by NRL and built by the Applied Research Laboratories
of the University of Texas, Austin (ARL:UT), the telescope consists of 16
antennas connected to a suite of electronics that combine the signals from
each antenna. Each antenna is only 4 feet tall and acts much like an old
style television antenna, receiving radio waves from many different
directions simultaneously. When combined, the data from the individual
antennas is comparable to that from a more traditional dish style telescope
with a diameter of 70 feet.

The antenna design, which resembles a household ceiling fan, with blades
that have drooped down at an angle of 45 degrees, was conceived to allow the
array to see the full sky and cover a wide range of frequencies with a
single antenna "The sophisticated digital electronics used in the LWDA allow
it to change observing frequency or point in a new direction in an instant,
and even allow it to look in two directions at the same time," says Dr. Paul
Ray, an astrophysicist at NRL who is overseeing the overall performance of
the LWDA.

When completed, the LWA will operate in a similar manner, but on a much
grander scale. Plans call for over 13,000 individual antennas, divided into
50 stations. These stations will be spread over a 250-mile area across New
Mexico, and possibly beyond. Dr. Ray explains, "With so many antennas
required for the final LWA, it is vital that we have a testbed on which we
can demonstrate the performance of a small number of them before
construction of the full LWA begins in earnest." NRL's LWDA serves this
purpose, allowing the astronomers and engineers to test the dipole antennas
and related computer hardware and software on a small scale, before
embarking on construction.

The LWA, funding for which is managed by the Office of Naval Research, is a
project of the Southwest Consortium, led by the University of New Mexico,
and including NRL, ARL:UT, and Los Alamos National Laboratory, with
important contributions from Virginia Tech and cooperation from the National
Radio Astronomy Observatory (NRAO). The NRAO is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc.

Related visuals,
http://www.nrl.navy.mil/pressRelease...=15-07r#images