Project Website http://www.haystack.mit.edu/ast/science/uig/index.html
The process of galaxy formation is a central element of the evolution of the universe. It is now apparent that collisions between gas-rich galaxies play a pivotal role in the star formation history of the universe, and in determining the properties of the galaxies we see in the local universe. When two galaxies collide, large-scale momentum exchange occurs and substantial masses of gas and dust settle into the middle of the gravitational potential well of the merging system. The resulting dense nuclear concentration is an ideal environment for star formation, and the resulting fireworks generate bolometric luminosities which rival those of quasars. These galactic nuclei host frequent supernova explosions and a bewilderingly complex mixture of molecular gas, dust, high velocity outflows, and in many cases, supermassive black holes revealed by the presence of a quasar nucleus.
Principal obstacles to the detailed study of these sysytems are the extreme absorption and obscuration at most wavelengths, and the small angular extent of the regions where all the action is occurring. By using centimeter-wavelength radio astronomy, and VLBI, Haystack astronomers can see through the dust and gas to probe conditions inside the maelstrom. In the nearby merging galaxy system Arp 220, the radio signatures of 50 supernova explosions can be traced, and four new explosions have been observed in only a 12-month period. The same observations can also reveal the detailed properties of clouds of OH molecules, tracing the distribution and dynamics of the molecular gas on parsec scales.