June 20, 2000 Astronomers said a fond farewell to NASA's Compton Gamma Ray Observatory earlier this month. The Compton Observatory was instrumental in proving gamma-ray bursts come from the most distant reaches of the cosmos and are the most powerful explosions in the universe. A team led by scientists at NASA's Marshall Space Flight Center in Huntsville, Ala., is developing a new burst monitor to fly on Compton's successor -- the Gamma Ray Large Area Space Telescope, or GLAST -- planned for launch in 2005.
The GLAST Burst Monitor -- working with GLAST's main instrument, the Large Area Telescope -- will provide the broadest energy coverage ever available on a single spacecraft for gamma-ray studies. Together, the two instruments will observe gamma rays with the lowest energies to those with the highest energies.
"We want to discover how these bursts light up the universe with such a tremendous amount of energy," said Dr. Charles Meegan, a Marshall Center astrophysicist and the principal investigator for the project. "We want to determine the nature of gamma-ray bursts -- still one of the greatest mysteries of astrophysics."
To design the new instrument, Marshall Center scientists will draw on more than two decades of experience building and operating the Burst and Transient Source Experiment -- also known as BATSE -- one of four instruments on the Compton Observatory. During its productive nine-year life, BATSE observed more than 2,500 gamma-ray bursts, but astronomers are still puzzled about the nature of these illusive objects.
"The total amount of energy emitted by all the stars in our galaxy is not as much energy as that released by one gamma-ray burst in a few seconds," said Meegan. "In 10 seconds, a gamma-ray burst can discharge thousands of times more energy than our Sun will ever give off in its entire lifetime. Scientists have had trouble figuring out just what could cause such violent blasts coming from all parts of the universe."
Meegan, who enjoys working all types of puzzles, is eager to lead a team to build an instrument capable of solving the mystery surrounding gamma-ray bursts. Many questions remain for the team to investigate.
What is the source of explosions emitting most of their energy in gamma rays - the highest energy radiation, even more powerful than X-rays? How are the explosions created? Have these blasts influenced Earth over the course of the planet's history?
"To find out what is causing these explosions, we will use the GLAST Burst Monitor to observe most of the energy released by a burst, while the primary telescope detects the very highest energy gamma rays emitted during the blast," said Meegan.
When a burst occurs, the GLAST Burst Monitor will detect gamma rays from the burst and identify the location of the burst quickly. Then, computers will use this information to automatically point the Large Area Telescope toward the burst. Working in concert, the GLAST instruments will see energy from a few thousand electron volts to billions of electron volts. By recording over an energy range hundreds of times larger than that detected by BATSE, astronomers may come closer to finding out what causes these explosions.
Are the explosions the birth announcement of a black hole -- a collapsed star with gravity so strong that it devours other objects and not even light can escape? Or are they the death of a neutron star -- a tiny star made of material so heavy that a sugar cube-sized piece can weigh as much as a billion tons? Scientists don't know.
"We are witnessing something dramatic in the life of an astronomical object," said Meegan. "Our experience with BATSE showed us that if you try to predict what it is without data, you'll be wrong. If bursts have done any thing, they have made scientists humble."
To design the best instrument, Meegan has assembled a team that includes scientists from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who are collaborating with NASA through an agreement with the German Space Agency. The Max Planck Institute will build crystal detectors -- the monitor's main component for intercepting gamma rays. Scientists from the Marshall Center and the University of Alabama in Huntsville will provide the flight electronics and software for the instrument.
The project also will be an opportunity for the next generation of gamma-ray astronomers to learn how to build a major scientific instrument. The team includes many young astronomers -- who began their careers by analyzing BATSE data -- from the Marshall Center and the University of Alabama in Huntsville.
Goddard Space Flight Center in Greenbelt, Md., will manage the GLAST mission for NASA's Office of Space Science in Washington, D.C.
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The above story is based on materials provided by NASA/Marshall Space Flight Center.
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