Astronomy

Spiral Fueling of a Black Hole

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Science  07 Apr 2000:
Vol. 288, Issue 5463, pp. 13
DOI: 10.1126/science.288.5463.13f

Seyfert galaxies are large spiral galaxies with a bright nucleus. The nucleus is thought to hide an active black hole, on the basis of the observed strong infrared, x-ray, and gamma ray emissions. Understanding how a black hole is fed—that is, how the black hole accumulates enough gas and dust from its surrounding galaxy to fuel its energetic engine—remains an astrophysical puzzle.

Martini and Pogge obtained near-infrared images with the NICMOS camera on Hubble Space Telescope (HST) of 24 Type 2 Seyfert galaxies (Type 2s contain a galactic bulge of molecular gas near the nucleus of the galaxy), and they combined these images with archived optical images taken with WFPC2 on HST to get to the center of the feeding frenzy. Most of the Seyfert galaxies have a centrally located series of dust lanes creating a nuclear spiral that seems to be connected to the center but is clearly detached from the major spiral arms of each galaxy. Estimates of the amount of dust in the nuclear spirals suggest a minimum of a million solar masses of material, more than enough to support the activity of a black hole. Furthermore, the spirals are multi-arm pinwheels, which indicates that they did not form due to gravitational instabilities in self-gravitating disks; instead these nuclear spirals may have formed by the propagation of shock waves, which would reduce the angular momentum of the gas in the accretion disk.—LR

Astron. J.118, 2646 (1999).

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