Laser guide star crucial to imaging unusual gravitational lens

July 16, 2010

Astronomers at the California Institute of Technology and Ecole Polytechnique Fédérale de Lausanne have discovered the first known case of a distant galaxy being magnified by a quasar acting as a gravitational lens.

John Wallace

This image of the first-ever foreground quasar (blue) lensing a background galaxy (red) was taken with the Keck II telescope using sodium laser guide-star adaptive optics.

Pasadena, CA--Astronomers at the California Institute of Technology and Ecole Polytechnique Fédérale de Lausanne (Lausanne, Switzerland) have discovered the first known case of a distant galaxy being magnified by a quasar acting as a gravitational lens.¹ The discovery is based in part on observations done at the W. M. Keck Observatory on Hawaii's Mauna Kea, relying on its laser guide-star adaptive optics (AO). The Keck Observatory has been an astronomy leader in the use of laser guide-star AO.

The quasar is the lens

Quasars, which are extraordinary luminous distant objects, are thought to be powered by supermassive black holes in the cores of galaxies. A single quasar could be a thousand times brighter than an entire galaxy of a hundred billion stars, which makes studies of their host galaxies exceedingly difficult. The significance of the discovery, the researchers say, is that it provides a novel way to understand these host galaxies (details of the host galaxy can be calculated from the shapes of the misshapen gravitationally focused images of the further object).

Hundreds of cases of gravitationally lensed quasars gravitationally lensed by closer galaxies are now known—but, until the current work, the reverse process (a background galaxy being lensed by the massive host galaxy of a foreground quasar) had never been detected.

To find the cosmic lens, the astronomers searched a large database of quasar spectra obtained by the Sloan Digital Sky Survey (SDSS) to select candidates for "reverse" quasar-galaxy gravitational lensing. Follow-up observations of the best candidate--quasar SDSS J0013+1523, located about 1.6 billion light years away--using the Keck Observatory's 10 meter telescope, confirmed that the quasar was indeed magnifying a galaxy located about 7.5 billion light years away.

The optical output of sodium guide-star lasers is growing by leaps and bounds and has already reached several tens of watts continuous-wave.

REFERENCE:

1. F. Courbin et al., Astronomy & Astrophysics, published online 16 July 2010; DOI: 10.1051/0004-6361/201014376

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.