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April 7, 2004

Purdue scientists help construct telescope for black holes, pulsars

WEST LAFAYETTE, Ind. - A trio of Purdue University physicists are making key contributions to a new telescope designed to study some of the most exotic and energetic objects in the universe, from quasars and supernova remnants to the massive black holes at the centers of galaxies.

VERITAS gamma-ray telescope
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The group - professors John Finley and Wei Cui, and emeritus professor James Gaidos - are developing systems for use in VERITAS, a gamma-ray observation facility on Kitt Peak in southern Arizona on which construction was recently started. VERITAS, which stands for Very Energetic Radiation Imaging Telescope Array System, could help astronomers answer fundamental questions about the cosmos.

"This will be one of the most sensitive very-high-energy gamma-ray observatories in the world, and certainly the most sensitive in the United States," said Finley, who is Purdue's representative to the telescope's executive committee. "Data this telescope collects could give insights into issues now under intense scientific debate - such as the nature of dark matter and when galaxies formed in the early universe."

The telescope will comprise an array of four 12-meter diameter optical reflectors, each with an ultra-fast camera. The target date for completion of the $13.1 million facility is October 2006.

Each Purdue scientist is contributing to a different part of the telescope. Cui (pronounced CHOO-ee), as software group leader, is developing the programs that will sift through and analyze the images the telescope collects, while Gaidos is subproject leader in charge of the arrays of mirrors that will focus the gathered light. Finley is leading the subproject in charge of calibrating the focal plane optical sensors called photomultiplier tubes. These devices can detect the flashes of light that appear high above the Earth when gamma rays from a distant source interact with the upper atmosphere.

"These photomultipliers are similar to those in use in particle accelerators around the world," Finley said. "Only instead of trying to detect showers of artificially-produced particles inside a laboratory, the tubes in VERITAS will detect natural collisions that occur when a very high-energy gamma ray from a distant source strikes molecules in the air."

The technique used to detect these gamma rays was pioneered at the Smithsonian's Whipple Observatory using the 10-meter optical reflector built in 1968. Very high-energy gamma rays (photons with energy of a million to a billion times the energy of a photon of visible light) interact with the upper atmosphere and initiate a cascade, or shower, of particles. The showers lead to a short burst of blue light. The Whipple group recorded the image of the cascade of particles and showed it was possible to identify those initiated by gamma rays from the much more numerous background flashes produced by charged cosmic rays.

"VERITAS will have a sensitivity that exceeds that of the existing Whipple telescope by a factor of 10," Finley said. "It is anticipated that more than a hundred sources will be detected."

All these observations will generate vast quantities of raw information requiring analysis.

"Once we begin collecting and analyzing data, we hope to explore such high-energy emitters as pulsars, supernova remnants, X-ray binaries, black holes, active galactic nuclei and gamma-ray bursts," Finley said. "Additionally, these cosmic particle accelerators may make possible the investigation of new physics at extreme energies, which are beyond the reach of accelerators built on Earth."

VERITAS will be located in Horseshoe Canyon at the 5,800-foot level on Kitt Peak. This site provides high altitude and easy access with excellent shielding from artificial lights. The facility will come into operation prior to the 2007 launch of NASA's Gamma-ray Large Area Space Telescope (GLAST). Together the two telescopes will make observations of cosmic gamma rays and could greatly extend our knowledge of the universe, Finley said.

Purdue is part of the VERITAS Collaboration, which includes seven institutions in the United States and three institutions in Canada, Ireland and the U.K.

In addition to funding from the Department of Energy and National Science Foundation, the project receives support from the Smithsonian Institution, the Particle Physics and Astronomy Research Council in the U.K., Enterprise-Ireland in Ireland and the Natural Sciences and Engineering Research Council in Canada.

Writer: Chad Boutin, (765) 494-2081,

Source: John Finley, (765) 494-5048,

Purdue News Service: (765) 494-2096;

Shown is an illustration of the VERITAS gamma-ray telescope now under construction on Kitt Peak in Arizona. The telescope will permit astronomers to examine some of the most energetic objects in the universe, from quasars to the massive black holes thought to exist at the centers of galaxies. The illustration has been prepared by superimposing four copies of a photograph taken of a single dish antenna onto the landscape where the telescope will be located after its completion in October 2006. (Illustration/VERITAS Collaboration)

A publication-quality illustration is available at

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