SETI [ASTRO] Astronomers' Do-It-Yourself Project Opening A New Window on the Universe


Larry Klaes (lklaes@bbn.com)
Mon, 07 Jun 1999 20:57:49 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Mon, 7 Jun 1999 19:17:48 GMT >From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> >To: astro@lists.mindspring.com >Subject: [ASTRO] Astronomers' Do-It-Yourself Project Opening A New Window on the Universe >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> > >National Radio Astronomy Observatory >P.O. Box O >Socorro, New Mexico 87801 >http://www.nrao.edu > >Contact: >Dave Finley, Public Information Officer >(505) 835-7302 dfinley@nrao.edu > >FOR RELEASE: May 31, 1999 > >Astronomers' Do-It-Yourself Project Opening A New Window on the Universe > >Rolling up their sleeves to build and install new equipment for the National >Science Foundation's (NSF) Very Large Array (VLA) radio telescope, a team of >astronomers has opened a new window on the universe, revealing tantalizing >new information about the explosions of massive stars, the workings of >galaxies with supermassive black holes at their centers, and clusters of >galaxies. > >"We're going back to the region of wavelengths where Karl Jansky started >radio astronomy in 1932," said Namir Kassim, of the Naval Research >Laboratory (NRL), in Washington, D.C. "This is one of the most poorly >explored regions of the electromagnetic spectrum, yet it offers tremendous >potential to learn exciting new information about everything from the Sun >and planets to galaxy clusters and the universe itself," Kassim said. > >Kassim, along with Rick Perley of the National Radio Astronomy Observatory >(NRAO) in Socorro, NM; William Erickson, a professor emeritus at the >University of Maryland; and Joseph Lazio, also of NRL, presented results of >their observations with the new VLA system at the American Astronomical >Society's meeting in Chicago. > >The new system uses the 27 dish antennas of the VLA, each 25 meters (82 >feet) in diameter, to receive cosmic radio emissions at a frequency of 74 >MHz, or a wavelength of about four meters. This frequency, lower than that >of the FM broadcast band, is far below the usual frequencies, 1- 50 GHz, >used for radio astronomy. "Though the region of 15-150 MHz is where Jansky >and Grote Reber did the first radio-astronomy work in the 1930s and 1940s, >it has long been neglected because of technical difficulties of working in >that region," said Perley. > >Still, the astronomers said, there is much to be learned by studying the >universe at these wavelengths. "There are phenomena associated with the Sun >and planets, with other objects in our own Milky Way Galaxy, and with other >galaxies and clusters of galaxies, and potentially ancient emission from the >Universe itself that we can see only by observing at these longer >wavelengths," Kassim said. > >The results of their first observations with the new VLA system have proven >their point. Aiming the VLA at the supernova remnant Cassiopeia A, the shell >of debris from a giant stellar explosion, they found evidence for cool gas >inside the shell that has not yet been shocked by the "reverse shock" that >propagates backwards through the "ejecta" towards the explosion's center > >"We know how old this supernova remnant is -- about 300 years -- and >whether or not the reverse shock would have passed through all the ejecta >yet depends on the nature of the star that exploded and the characteristics >of its winds and surroundings before its death," Kassim said. "Finding >unshocked gas inside this remnant, the first direct case for such material >detected in the radio part of the spectrum, confirms the predictions of >supernova evolution theory and thereby advances them." > >Other observations showed giant, radio-emitting "bubbles" in the galaxy M87 >in the constellation Virgo. These objects, also seen with the VLA at the >somewhat higher frequency of 330 MHz, raised questions about how old they >were and how they were powered, as well as how they are linked to the even >larger halo of X-ray emission generated around this galaxy. "The shape and >extent of these huge, radio-emitting regions suggests that they are >relatively young, expanding, and are being powered by particles shot out of >the galaxy's nucleus by the gravitational energy of a supermassive black >hole," said Kassim. "Comparison of the higher frequency images with our >new one made at 74 MHz show exactly the correspondence we would expect >if the black hole is powering these regions," he added. > >The researchers, together with astronomer Phillip Kronberg and his >collaborators from the University of Toronto, also looked at the Coma >Cluster of galaxies, some 450 million light-years distant. "There is a >radio-emitting halo around this cluster, and our image made at 74 MHz >greatly improves our knowledge of its extent and properties. This is crucial >to figuring out how the halo got there in the first place," Kassim said. > >In the region of the Coma Cluster, the scientists made a "super" wide-field >image. This image, showing an area some 15 degrees on a side, shows >hundreds of radio-emitting objects, including extremely distant galaxies. >Dubbed the "VLA Coma Deep Field," the image is "one of the most spectacular >made recently at the VLA," Kassim said. "The amount of information obtained >from only a single pointing of the VLA is awesome. Images like this will be >extremely valuable in learning about the early universe," he said. > >All of these results came about because of the astronomers' persistence in >pursuing a long-sought goal of equipping the VLA to observe at the new >frequency. Erickson has been a long-time proponent of low-frequency radio >astronomy. Both Perley and Kassim were Ph.D students of Erickson at the >University of Maryland. The 330-MHz capability, also supported by NRL, was >added to the VLA in the 1980s, and the group managed to install equipment >for 74 MHz on eight of the VLA's 27 antennas a few years ago. > >They still wanted all the antennas equipped, however. "We knew we could >use off-the-shelf components and equip antennas for about a thousand >dollars each," said Perley, "but we just couldn't seem to squeeze the loose >change out of anyone." > >Then Kassim pursuaded the Naval Research Laboratory to provide funding for >the project. The astronomers then went to work to get the most performance >for the money. Erickson, aided by NRL engineer Brian Hicks and Kassim, did >the actual construction of 74-MHz receivers at NRL. The astronomers also >worked alongside engineers and technicians, climbing on the VLA's giant >dish antennas to install the new equipment. Hicks is presently constructing >additional 74 MHz receivers at NRL for eventual tests on Very Long Baseline >Array antennas > >The result, Perley said, "is not bad for a do-it-yourself project." In the >first observing session using the new equipment, astronomers from four >continents studied a wide range of celestial objects, and the results "were >a spectacular success. We proved that you can make good images with the >VLA at this frequency. The problem always was the difficulty in processing >data to correct for ionospheric effects on the incoming radio waves. New >computing techniques now have solved that problem." > >"We have shattered the ionospheric barrier and solved the wide-field >imaging problem," Kassim said. > >The research results presented at the AAS meeting "show the great value of >this new capability," Kassim said. "In addition to our work on supernova >remnants, active galaxies and galaxy clusters, other papers presented at >this meeting show that this frequency range is extremely valuable for solar >research," Kassim added. > >"In fact, the success of the VLA at this frequency shows that we could learn >even more from this new window on the universe by building a much larger >and more sensitive instrument dedicated to long-wavelength radio >astronomy -- the Low Frequency Array (LOFAR). An international consortium, >initially involving NRL, NRAO, and the Netherlands Foundation for Radio >Astronomy, currently is forming to develop LOFAR, an instrument which >would see more detail and fainter objects than we can today," Kassim said. > >The VLA is an instrument of the National Radio Astronomy Observatory, a >facility of the National Science Foundation, operated under cooperative >agreement by Associated Universities, Inc. Basic research in radio astronomy >at the Naval Research Laboratory is supported by the Office of Naval >Research. > >



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