title: A 17-billion-solar-mass black hole in a group galaxy with a diffuse core.
abstract: Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day 'dormant' descendants of this population of 'active' black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall--the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600--a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.
authors.affiliation: Max Planck-Institute for Extraterrestrial Physics, Giessenbachstraße 1, D-85741 Garching, Germany.|Universitätssternwarte München, Scheinerstraße 1, D-81679 München, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Thomas
authors.affiliation: Department of Astronomy, University of California, Berkeley, California 94720, USA.
authors.forename: Chung-Pei
authors.initials: CP
authors.lastname: Ma
authors.affiliation: Dominion Astrophysical Observatory, NRC Herzberg Institute of Astrophysics, Victoria, British Columbia V9E 2E7, Canada.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: McConnell
authors.affiliation: Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Jenny E
authors.initials: JE
authors.lastname: Greene
authors.affiliation: Dominion Astrophysical Observatory, NRC Herzberg Institute of Astrophysics, Victoria, British Columbia V9E 2E7, Canada.
authors.forename: John P
authors.initials: JP
authors.lastname: Blakeslee
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Janish