Gamma Ray Astronomy
Gamma-ray astrophysics probes the cosmos at the highest energies, providing views of the universe relatively undiluted by thermal processes that dominate at lower energies. The discrete physical systems studied include relativistic jets emerging from accretion disks near black holes powering the nuclei of active galaxies, neutron-star powered supernova remants (plerions) and the remnant shock waves from supernova thought to be the origin of galactic cosmic rays. (A few pictures are shown below.) The Iowa State University gamma-ray astrophysics group has primary roles in the development and operation of the VERITAS ground-based array of telescopes and is also involved with the GLAST satellite telescope.
The X-ray picture on the right is Cassiopeia A , a ~340 year old supernova remnant. It was recorded with the Chandra satellite. Low, medium and higher X-ray energies are represented by as red, green and blue respectively. The picture shows remarkable structure (e.g., jets) in the explosion debris and a compact object at the center, which may be a neutron star.
At higher photon energies (~10 to 10,000 MeV) the EGRET instrument aboard the Compton Gamma-ray Observatory was used to make a number of spectacular discoveries including high energy emission from blazars (extremely luminous centers of galaxies powered by massive, accreting black holes), pulsars (compact, dense, magnetized rotating neutron stars) and enigmatic "undentified" objects. The EGRET all sky map on the right clearly shows both galactic objects (in the plane) and extragalactic objects. The GLAST satellite detector will be the EGRET successor with greatly improved sensitivity.
At higher energies, ground-based Cherenkov-light imaging telescopes are sensitive to energies greater than about 100 GeV. These are the highest energies at which discrete objects have been observed in nature. Supernova remnants (both plerions and shell-type) and blazars have been discoved at these energies. The imaging technique was pioneered by the Whipple Collaboration (now the VERITAS collaboration) that is constructing an array of these telescopes in southern Arizona.