With new telescope, a fresh view of the cosmos

A spacecraft called GLAST is set to open a new window on the high-octane cosmos.

The orbiting observatory, designed to detect high-energy gamma rays, is slated for launch perhaps as early as June 11. It’s designed to explore the most energetic, exotic phenomena the universe has to offer. These range from tight beams of particles hurtling across vast distances from the center of young, active galaxies to the more fleeting gamma ray bursts thought to occur when neutron stars collide or an exploding star collapses to form a black hole.

Compared with the often sedate views of stars and galaxies astronomers gather through optical telescopes, “with GLAST, it’s like the Fourth of July all over the sky,” says Peter Michelson, a physicist at Stanford University in Palo Alto, Calif.

GLAST, or Gamma-ray Large Area Space Telescope, may also yield new insights into the nature of so-called dark matter, which constitutes 80 percent of matter in the universe. In principle the data GLAST collects could also provide a test of quantum theories of gravity – the missing link in efforts to demonstrate that the four forces of nature are low-energy manifestations of one unified force present at the universe’s birth.

A project across borders
The $690 million mission represents a deepening collaboration among astrophysicists and particle physicists.

For years, each group has asked related questions about the origin and evolution of the universe. Particle physicists probe the very tiny with large underground particle accelerators. They try to re-create conditions and subatomic particles thought to have existed at the earliest moments of the universe’s birth.

Astrophysicists explore the universe on cosmic scales with ground-and space-based instruments, reaching back ever earlier toward the universe’s infancy. Now, both are set to add a new common tool to their arsenal.

GLAST’s hardware reflects this collaboration, a joint mission between the National Aeronautics and Space Administration and the US Department of Energy and scientists overseas. The gamma ray detectors and analysis software trace their pedigree to projects such as the defunct Superconducting Super Collider and the new Large Hadron Collider at the European Organization for Nuclear Research (CERN) in Geneva. The burst monitor, designed to scan broad swaths of sky for the events, comes from NASA’s Marshall Spaceflight Center and the Max Plank Institute for Extraterrestrial Physics in Germany. [Editor's Note: This paragraph has been updated to clarify CERN’s influence on the detectors’ design.]

During a mission that could last up to 10 years, scientists say they expect to gain deeper insights into the cosmic cataclysms that generate gamma rays at the high energy levels GLAST is designed to detect.

High on the list of things scientists are hoping to see are gamma ray bursts, which by some estimates unleash as much energy in a few seconds as all the energy the sun will emit during its expected 10-billion-year existence. In the 1960s, satellites watching for nuclear weapons tests first discovered the bursts. The events have remained enigmatic ever since.

The bursts are thought to come from stars exploding as supernovae, among other sources. Modeling studies suggest that a collapsed star’s amped-up spin and its magnetic field combine to focus and sling jets of material into space at nearly the speed of light, generating a tight beam of high-energy gamma rays in the process. Researchers remain puzzled over the kinds of stars that generate these bursts and the physical mechanisms producing the gamma rays – in part, because they’ve seen so few to date.

But GLAST is 50 times more sensitive than its predecessor, the Compton Gamma Ray Observatory. Moreover, its wider field of view allows it to scan the whole sky every two days, instead of every 15 months.

Over the course of the mission, researchers expect to add hundreds of these bursts to the handful in their archives, notes Dr. Michelson, the lead scientist on one of the orbiter’s two instruments. Many bursts are expected to be distant enough to serve as probes of the early universe.

Another target: blazars or marathon gamma ray bursts. Blazars are thought to come from supermassive black holes at the centers of young, active galaxies.

“A blazar episode lasts for 10 million to 100 million years,” explains Alan Marscher, an astrophysicist at Boston University who heads the university’s blazar research group. In the process, they generate telltale jets of particles that stretch into space for 10 million to 100 million light-years. Data from GLAST, combined with information from radio-telescopes and visible light, will help scientists tease out the processes behind these galactic beacons.

Heart of the matter
GLAST also could take its team into Nobel Prize territory in its exploration of dark matter. No one has seen the stuff directly. Its presence was initially inferred from its gravitational effects on galaxies: Without it, galaxies would fly apart.

The leading candidate for dark matter is thought to belong to a class of particles dubbed WIMPs, for weakly interacting massive particles. Theories predict that when two of these particles meet, they annihilate each other in a burst of energy detectable as gamma rays. The energy the gamma rays carry allows physicists to calculate the WIMPs’ masses. Dark matter candidates fall into a mass range that would yield gamma rays GLAST is designed to detect.

This indirect measure would also serve as a tool for mapping the dark-matter “halo” coralling the Milky Way.

Dr. Peskin says that with complementary measurements likely to come from GLAST and CERN’s collider, don’t be surprised if physicists finally detect and unravel some of dark matter’s mysteries within the next five years. “That will be exciting to see,” he says.