A pulsar, as seen by NASA's Chandra X-ray Observatory. Image Credit: NASAGamma rays sound like the stuff of a superhero adventure, a deadly force used by the villain to wreak havoc across the planet. Indeed, gamma rays -- a highly energetic form of radiation given off by many objects in space -- would be quite harmful to life on Earth. Fortunately, Earth's atmosphere acts as the superhero, absorbing gamma rays before they reach the ground.
-- Black holes are spherical regions formed in space when a massive star dies, collapsing from its own gravity. The largest black holes -- known as supermassive black holes -- seem to be different in nature from their smaller counterparts. Many scientists now believe that supermassive black holes -- thought to be at the centers of most galaxies -- were created with those galaxies when they were first formed.
An artist's impression of a supermassive black hole at the center of a galaxy. Image Credit: NASA/MAXIM
It's anticipated that GLAST will help answer questions about the jets of matter that are ejected outward from supermassive black holes at nearly the speed of light. GLAST will be able to see the gamma rays emitted by these jets, but only when the jets are pointed toward the spacecraft. Scientists are curious about how the jets form and how the matter is accelerated to such a high speed. Data collected could also shed light on the role of supermassive black holes in the formation and evolution of galaxies.GLAST will also study solar flares and cosmic rays, both of which produce gamma rays and can impact Earth's atmosphere. The spacecraft could also discover entirely new sources of gamma-ray radiation.
-- While the most massive stars end their life cycle by collapsing into black holes, slightly less massive stars do not collapse all the way to black holes. Instead, they end their lives as neutron stars. Although not as extreme as a black hole, a neutron star is still incredibly dense -- with the entire mass of a large star compressed into a ball of neutrons and other elementary particles about 20 kilometers (approximately 12 miles) wide. Rapidly rotating neutron stars, or pulsars, emit beams of gamma rays and other types of radiation from their magnetic poles. Instruments on Earth and in space detect the radiation as regular pulses -- thus the name pulsars -- every time a beam sweeps by.
Particles in the pulsar beams are accelerated to high speeds and emit gamma rays, similar to the jets of matter streaking away from supermassive black holes. GLAST will have the tools needed to provide information about how pulsars emit radiation and, possibly, to learn more about how particles in the beams are accelerated.
-- Gamma-ray bursts, or GRBs, are sudden and intense bursts of gamma rays lasting from a few milliseconds to several minutes. About two GRBs are detected by satellites each week. Scientists have determined that GRBs originate from beyond the Milky Way galaxy. Recent evidence indicates that many GRBs may be generated by the collapse of massive stars into black holes. Others may be caused by colliding neutron stars or the merger of a neutron star and a black hole, both of which result in the birth of a black hole.
The GLAST telescope and a complementary instrument called the GLAST Burst Monitor are designed to detect GRBs over a wider energy range than previous instruments. These observations could provide important information about the mechanisms that trigger GRBs, and could reveal additional details about the bursts and their aftermath.
An X-ray image of a gamma-ray burst. Image Credit: ESAGLAST is a joint project between NASA, the U.S. Department of Energy, and institutions in France, Germany, Japan, Italy and Sweden, and is being built by General Dynamics.