RELEASE: 00-197

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

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.



Steve Roy

Media Relations


(256) 544-0034