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Sketch of a thin accretion disc spinning around a black hole. (NASA/Dana Berry, SkyWorks Digital)

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Prof. Dr. Wolfram Kollatschny

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Press release: Black holes may be up to ten times smaller than previously assumed


Nr. 29/2011 - 24.02.2011


Research results from Göttingen enable more precise determination of mass

Black holes may be up to ten times smaller than has been estimated so far. Astrophysicists at the University of Göttingen reach this conclusion in a study that appeared on Thursday, 17th February 2011 in the prominent scientific journal Nature. Located at the centre of galaxies, super-massive black holes have a mass of up to a billion times the mass of the Sun. They are surrounded by a so-called accretion disc, in which the central galactic material collects. Due to the strong pull exerted by the black hole, material at its inner perimeter falls in at extremely high velocity. The researchers have analysed the light emissions of a total of 37 galaxies and were able for the first time to measure accurately the rotation speed of the disc material. Using Kepler’s third law, the mass of the black hole can be calculated on the basis of the rotation speed and the distance between the bodies. The masses derived from these calculations are far smaller than was previously assumed and since the mass of a black hole is proportional to its size, they are hence smaller than was estimated.

The scientists registered rotation speeds of between several hundred and several thousand kilometres per second. In the inward direction, that is towards the black hole, the speed increases – analogous to this, the planets more central in our sun system move more quickly than the outer ones. The Göttingen astrophysicists were further able to make statements for the first time about the geometry of the material clouds surrounding a black hole: at high rotation speeds the surrounding material is arranged in the form of a flat disc, while in the case of slowly rotating holes the arrangement takes the form a thick disc.

Publication: Wolfram Kollatschny, Matthias Zetzl. Broad-line active galactic nuclei rotate faster than narrow-line ones. Nature. DOI: 10.1038/nature09761.