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Old news on quasar viscosity

Nature Astronomy volume 2, page 504 (2018)Cite this article

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An Author Correction to this article was published on 10 July 2018

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To the Editor — Much of the active galactic nuclei and quasar community has been fixated on a particular model for the energetically dominant ‘Big Blue Bump’ component of the spectral energy distribution for the past 40 years1,2, despite the fact that the model is qualitatively incorrect. It’s a ‘quasi-static’ model, meaning that flow of matter through the disk is steady on human timescales, except for the very lowest luminosity cases, with gas elements migrating through a geometrically thin accretion disk towards the black hole; the rate is constant over periods that are long compared with any other timescale in the problem, or a human lifetime. But empirically, variations in flux were known to occur on timescales of weeks to months, nearly in phase throughout the optical and ultraviolet regions, so cognitive dissonance was a part of the theory from the get-go.

In a recent Comment titled ‘Quasar viscosity crisis’, Andy Lawrence3 points out that the variability properties of quasars rule out the model. Enough was known about quasar variability to preclude application of the model at the time it was proposed, and the failings of the model were decisively documented and explained by Alloin et al.4. The new variability data alluded to in Lawrence’s article are immaterial; the arguments made in many papers over the decades, starting with Alloin et al., were robust, with orders of magnitude to spare. Hence, although Lawrence was correct3, he wasn’t reporting any news. It would have been news in the early 1980s.

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Change history

  • 10 July 2018

    In the version of this Correspondence originally published, the wrong paper was given for ref. 1; instead of ‘Shields, G. A. Nature 273, 519–520 (1978)‘ it should have been ‘Shields, G. A. Nature 272, 706–708 (1978)’. This has now been corrected.

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  1. Department of Physics, University of California, Santa Barbara, CA, USA

    Robert Antonucci

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Antonucci, R. Old news on quasar viscosity. Nat Astron 2, 504 (2018). https://doi.org/10.1038/s41550-018-0521-1

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