Annual Report 2001 - Cornell University
003 Selected Faculty Research

04 Detecting Galaxy Collisions

Riccardo Giovanelli, Astronomy, and research staff Jeremy Darling, using the radio telescope at Arecibo Observatory, discovered 50 extragalactic objects called OH megamasers (radio beacons). An upgrade to Arecibo, the world's most sensitive radio telescope, allows it to pick up strong radio signals emitted when galaxies collide. Astronomers first observed masers (microwave amplification by stimulated emission of radiation) in the Milky Way in 1965, where they are associated with stars shrouded in molecular gas. When galaxies collide, masers can be a million times stronger than regular masers. These are called megamasers. The first known megamaser was discovered in 1982 at Arecibo. OH (oxygen-hydrogen) megamasers may provide clues to understanding the physics of the formation of galaxies. Astronomers can use the OH megamaser detection rate to measure the frequency of galaxy mergers throughout the history of the universe.

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