A fast and long-lived outflow from the supermassive black hole in NGC 5548

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Science  04 Jul 2014:
Vol. 345, Issue 6192, pp. 64-68
DOI: 10.1126/science.1253787

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Gas jets block extragalactic x-rays

Supermassive black holes at the heart of active galaxies produce powerful gas outflows. NGC 5548 is one such source known to sustain a persistent outflow of ionized gas. However, its associated x-ray and ultraviolet (UV) emission seem to have been suppressed in recent years. Kaastra et al. conducted a multiwavelength monitoring campaign throughout 2013 to characterize the system's behavior. They suggest that an additional faster jet component has been launching clumps of gas that obscure both the x-ray and UV radiation. The timing of this phenomenon indicates a source only a few light-days away from the nucleus. This proximity suggests that the outflow could be associated with a wind from the supermassive black hole's accretion disk. Even more powerful outflows could also influence their host galaxies, and this finding demonstrates how that feedback might work.

Science, this issue p. 64


Supermassive black holes in the nuclei of active galaxies expel large amounts of matter through powerful winds of ionized gas. The archetypal active galaxy NGC 5548 has been studied for decades, and high-resolution x-ray and ultraviolet (UV) observations have previously shown a persistent ionized outflow. An observing campaign in 2013 with six space observatories shows the nucleus to be obscured by a long-lasting, clumpy stream of ionized gas not seen before. It blocks 90% of the soft x-ray emission and causes simultaneous deep, broad UV absorption troughs. The outflow velocities of this gas are up to five times faster than those in the persistent outflow, and, at a distance of only a few light days from the nucleus, it may likely originate from the accretion disk.

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