Earth-sized virtual radio telescope developed
Posted: October 2, 2002

Astronomers have created an Earth-sized virtual radio telescope that can detect features 3,000 times smaller than the Hubble Space Telescope can see.

The virtual device, which was created by linking signals from radio telescopes on several continents, is the first to operate at shortest-ever (2 millimeter) radio wavelengths.

Credit: MIT
The international collaboration involves two telescopes in Arizona -- the Heinrich Hertz Submillimeter Telescope (HHT)on Mount Graham and the Kitt Peak 12-meter Telescope -- and telescopes in Spain, Finland, and Chile.

"Both the distance between partner telescopes and the ability to detect shorter wavelength, higher frequency radio emission gives this telescope its unprecedented power," said Lucy Ziurys, director of the Arizona Radio Observatory, part of the University of Arizona's Steward Observatory in Tucson.

Astronomers define telescope power is terms of angular resolution -- the ability to clearly separate two closely spaced objects in the sky. At its record-breaking best, the new telescope resolved an angle of 50 micro arc seconds, or about one hundred millionth of a degree of the sky.

"The resolution achieved by this telescope is the equivalent of sitting in New York and being able to see the dimples on a golf ball in Los Angeles," said Sheperd Doeleman of the Massachusetts Institute of Technology's Haystack Observatory.

Ziurys, Doeleman, Thomas Krichbaum of the Max-Planck-Institute for Radio Astronomy in Bonn, Germany, and Albert Greve of the Institut de Radioastronomie Millemetrique (IRAM), which operates telescopes in Granada, Spain, and Grenoble, France, are principal collaborators on the project. Finland's Metsahovi Radio Observatory, the European Southern Observatory's Swedish-operated SEST telescope, and the National Radio Astronomy Observatory are also involved. The National Science Foundation and the Tucson-based Research Corporation help fund the U.S. effort.

The world's most powerful radio telescope began to materialize late last year, when Greve, Ziurys, and Doeleman agreed to attempt 2mm-wavelength observations using Kitt Peak's 12-meter telescope and Mount Graham's HHT as the U.S. component of the international telescope array.

"At that time, we didn't have the capability to do 2mm observations at the HHT," Ziurys said. "We could build the devices, but we weren't sure we could do it by April, when the observing was scheduled for MIT."

But thanks to Arizona Radio Observatory chief engineer Henry Fagg, the HHT had its 2mm detector by April.

The astronomers first linked the two Arizona telescopes, which are separated by 100 miles, in 2mm radio observations, Ziurys said. They then tackled the bigger challenge of linking the U.S. telescopes to Europe. The two Arizona telescopes and one in Spain provided key long distance detections that were especially critical to the project.

The telescope has successfully picked up radio signals from galaxies more than 3 billion light years away. It will be used to study one of the fundamental mysteries of modern astronomy -- how so-called "active" galaxies produce their incredible energetic output.

Normally, galaxies emit as much energy as the sum of their stars. "Active" galaxies emit far more energy than the sum of their stars. The excess energy is concentrated at the galaxy's core. Astronomers believe that super massive black holes, billions of times bigger than the sun, power these energetic cores. Some of the cores spew powerful streams of high-speed particles millions of light years beyond their host galaxies. But how these high-speed particle jets are launched from galactic cores is not clear. The new telescope is specifically designed to make detailed images of where the jets erupt.

The technique of using several telescopes on different continents to simultaneously record radio emissions from the same object is called Very Long Baseline Interferometry (VLBI). Signals from each telescope are time-stamped with extremely accurate atomic clocks, recorded on magnetic tapes, then combined in a special-purpose supercomputer. The technique forms a virtual radio telescope that can be as large as the diameter of Earth.

Future plans are to direct the powerful new telescope at the core of the Milky Way Galaxy to detect structures close to our galaxy's suspected black hole.

"We weren't sure we could get it to work last spring, but clearly these current results represent just the tip of the iceberg," Ziurys said. "We are very excited about future science using this powerful technique."

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