Letters to Nature

Nature 400, 539-541 (5 August 1999) | doi:10.1038/22972; Received 23 February 1999; Accepted 17 June 1999

A geometric distance to the galaxy NGC4258 from orbital motions in a nuclear gas disk

J. R. Herrnstein1,2, J. M. Moran2, L. J. Greenhill2, P. J. Diamond1,3, M. Inoue4, N. Nakai4, M. Miyoshi5, C. Henkel6 & A. Riess7

  1. National Radio Astronomy Observatory, PO Box O, Socorro, New Mexico 87801, USA
  2. Harvard-Smithsonian Center for Astrophysics, Mail Stop 42, 60 Garden Street, Cambridge, Massachusetts 02138, USA
  3. Merlin and VLBI National Facility, Jodrell Bank, Macclesfield, Cheshire SK11 9DL, UK
  4. Nobeyama Radio Observatory, National Astronomical Observatory, Minamimaki, Minamisaku, Nagano 384-13, Japan
  5. VERA Project Office, National Astronomical Observatory, Mitaka, Tokyo, 181-8588, Japan
  6. Max Planck Institut für Radioastronomie, Auf dem Hugel 69, D-53121, Bonn, Germany
  7. Department of Astronomy, University of California at Berkeley, Berkeley, California 94720, USA

Correspondence to: J. R. Herrnstein1,2 Correspondence and requests for materials should be addressed to J.R.H. at NRAO (e-mail: Email: jherrnst@nrao.edu).

The accurate measurement of extragalactic distances is a central challenge of modern astronomy, being required for any realistic description of the age, geometry and fate of the Universe. The measurement of relative extragalactic distances has become fairly routine, but estimates of absolute distances are rare1. In the vicinity of the Sun, direct geometric techniques for obtaining absolute distances, such as orbital parallax, are feasible, but such techniques have hitherto been difficult to apply to other galaxies. As a result, uncertainties in the expansion rate and age of the Universe are dominated by uncertainties in the absolute calibration of the extragalactic distance ladder2. Here we report a geometric distance to the galaxy NGC4258, which we infer from the direct measurement of orbital motions in a disk of gas surrounding the nucleus of this galaxy. The distance so determined—7.2 plusminus 0.3 Mpc—is the most precise absolute extragalactic distance yet measured, and is likely to play an important role in future distance-scale calibrations.