Yale University - 2010 March 25
Black Holes in the Universe Gain Weight and Light Up During Galaxy CollisionsSupermassive black holes found at the centers of distant galaxies undergo huge growth spurts as a result of galactic collisions, according to a new study by astronomers at Yale University and the University of Hawaii. Their findings appear in the March 25 edition of Science Express.
As massive, gas-rich galaxies in the distant universe collide, the central black hole feeds on gas that is funneled to the center of the merger. “As a result of the violent, messy collision, the black hole also remains obscured behind a ‘veil’ of dust for between 10 million and 100 million years,” said Priyamvada Natarajan, professor of astronomy at Yale and one of the paper’s authors. After that time the dust is blown away to reveal a brightly shining quasar—the central region of a galaxy with an extremely energetic, supermassive black hole at its center—that lasts for another 100 million years, the team found.
University of Hawaii: Institute for Astronomy: 2010 March 25
Major Galaxy Mergers and the Growth of Supermassive Black Holes in QuasarsGiant black holes in the centers of galaxies grow mainly as a result of intergalactic collisions, according to results presented by a group of astronomers led by Dr. Ezequiel Treister from the University of Hawaii, published in the March 25th issue of the international journal Science.
As gas clouds in galaxies are sucked into the central black hole, they emit vast amounts of radiation, giving rise to objects that astronomers call quasars. "We find that these growing black holes are originally hidden by large amounts of dust", Treister said, "but after 10-100 million years this dust is blown out by the strong radiation pressure, leaving a naked quasar, that is visible in optical wavelengths and keeps shining for another 100 million years".
Despite observed strong correlations between central supermassive black holes (SMBHs) and star-formation in galactic nuclei, uncertainties exist in our understanding of their coupling. We present observations of the ratio of heavily obscured to unobscured quasars as a function of cosmic epoch up to z = 3, and show that a simple physical model describing mergers of massive, gas-rich galaxies matches these observations. In the context of this model, every obscured and unobscured quasar represents two distinct phases that result from a massive galaxy merger event. Much of the mass growth of the SMBH occurs during the heavily obscured phase. These observations provide additional evidence for a causal link between gas-rich galaxy mergers, accretion onto the nuclear SMBH, and coeval star formation.