theory of galaxies
Despite a decade of efforts to find flaws in the unification theory of active galaxies, the theory correctly explains the exotic phenomena of accreting supermassive black holes, according to a Yale astronomer.
"Furthermore, the striking parallels between normal and active galaxies that have become apparent in the last few years suggest that there is a larger 'Grand Unification' at play. Apparently every galaxy goes through an active phase," said Meg Urry, professor of physics and director of the Yale Center for Astronomy and Astrophysics, at the American Astronomical Society meeting on May 26 in Nashville, Tennessee.
Urry said the Grand Unification theory predicts what objects should appear in very deep multi-wavelength views of the universe. "Most of the active galaxies in the early universe have been hidden from view until now," she said. "We predict there are far more hidden black holes than brightly shining active galaxies."
New multi-wavelength surveys involving unique space observatories provide a way to test the Grand Unification theory, she said. Three of the National Aeronautics and Space Administration (NASA) space observatories -- the Hubble Space Telescope and the Chandra X-Ray Observatory, both already in orbit, and the Space Infrared Telescope Facility, due to be launched in August -- are critically important because they allow very deep imaging from far-infrared to X-ray wavelengths, where active galaxies and star-forming galaxies radiate most of their energy, she said. Preliminary results from the first two observatories are encouraging, Urry added.
"The new challenge is to understand in detail how galaxy formation -- the gravitational collapse of a galaxy -- is tied to star formation in that galaxy and to accretion onto the black hole at its center," she said. "Now we think all these processes are happening simultaneously, in the same objects. As a galaxy forms and collapses under the weight of its own gravity, it stimulates both intense star formation and the dumping of gas and stars onto the seed black hole at the center of the gravitational potential well."
"The galaxy starts collapsing, makes stars and makes an active nucleus," Urry said. "The violent events of this collapse dump matter onto the black hole and this releases a lot of energy. All these wild things are happening at once."
-- By Jacqueline Weaver
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