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