Astron. Astrophys. doi:10.1051/0004-6361/201014376 (2010)

Brighter than a hundred billion stars combined, quasars — extremely energetic galactic nuclei — typically outshine and obscure everything in their vicinity. Now astronomers have spotted a quasar that acts as a gravitational lens, and have used this property to uncover information about the galaxy that it inhabits.

Malte Tewes at the Swiss Federal Institute of Technology (EPFL) in Lausanne and his colleagues sifted through more than 22,000 potential candidates to find the exotic object, which is about 490 megaparsecs away. With its strong gravitational pull, the quasar redirects and magnifies the light of a galaxy located almost exactly behind it, more than 2,300 megaparsecs away. By measuring the effect of the quasar on the distant galaxy's light, the researchers estimated that the quasar's host galaxy has about 22 billion times the mass of the Sun — a more precise number than could be obtained using previous methods. The technique could help to determine how galaxies form and evolve.