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One black hole or two? Dust clouds can explain puzzling features of active galactic nuclei

   Gaskell comments: "We've shown that a lot of mysterious properties of active galactic nuclei can be explained by these small dusty clouds causing changes in what we see."

  Co-author Peter Harrington, a UCSC graduate student who began work on the project as an undergraduate, explained that gas spiralling towards a galaxy's central black hole forms a flat "accretion disk", and the superheated gas in the accretion disk emits intense thermal radiation. Some of that light is "reprocessed" (absorbed and re-emitted) by hydrogen and other gases swirling above the accretion disk in the broad-line region. Above and beyond this is a region of dust.

  "Once the dust crosses a certain threshold it is subjected to the strong radiation from the accretion disk", said Harrington. The authors believe this radiation is so intense that it blows the dust away from the disk, resulting in a clumpy outflow of dust clouds starting at the outer edge of the broad-line region.

See:http://www.ras.org.uk/news-and-press/3131-one-black-hole-or-two-dust-clouds-can-explain-puzzling-features-of-active-galactic-nuclei
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