Cosmology and Particle Astrophysics
Cosmology is defined as the study of the structure and dynamics of the universe. Particle astrophysics is the study of how the smallest pieces of matter interact on the grand scale of the universe. One of the biggest mysteries plaguing both these fields of study is the nature of dark matter. There is strong evidence that the universe visible to us is only 10% of the total mass of the universe, in other words, 90% of the mass of the universe is invisible to us. Currently the only way to detect this so called dark matter is by its gravitational effects on visible matter. This image below shows how light from distant galaxies undergoes gravitational lensing by a massive cluster of galaxies called Abell 2218, which is closer to us. In this instance we know what is causing the lensing, but dark matter can also cause this effect if the matter is massive enough.
Hubble image of gravitational lensing around Abell 2218
One theory for what dark matter might be is a type of hypothetical particle called a weakly interacting massive particle, or WIMP. The theory predicts that WIMPs may interact and annihilate one another, producing gamma rays at specific energy levels in the process. If the theory is correct, then GLAST would be capable of observing this radiation from annihilation events in the galactic halo, helping to unravel the mystery of dark matter.
Another issue for GLAST to address is the isotropic (in all directions) high-energy gamma-ray background radiation detected by EGRET. It is suspected to be extragalactic in origin and much of this background radiation will likely be resolved by GLAST into individual AGNs. The other possibility is that the background radiation is truly diffuse and a remnant of an event in the early universe.