Astronomers by using NASA’s Hubble Space Telescope were able to find several examples
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of galaxies containing quasars, which act as gravitational lenses, amplifying and distorting images of galaxies aligned behind them. Quasars are among the brightest objects in the universe, far outshining the total starlight of their host galaxies. Quasars are powered by supermassive black holes. To find these rare cases of galaxy-quasar combinations acting as lenses, a team of astronomers led by Frederic Courbin at the Ecole Polytechnique Federale de Lausanne (EPFL, Switzerland) selected 23,000 quasar spectra in the Sloan Digital Sky Survey (SDSS). They looked for the spectral imprint of galaxies at much greater distances that happened to align with foreground galaxies. Once candidates were identified, Hubble’s sharp view was used to look for gravitational arcs and rings that would be produced by gravitational lensing. Quasar host galaxies are hard or even impossible to see because the central quasar far outshines the galaxy. Therefore, it is difficult to estimate the mass of a host galaxy based on the collective brightness of its stars. But have to say that gravitational lensing candidates are invaluable for estimating the mass of a quasar’s host galaxy because the amount of distortion in the lens can be used to estimate a galaxy’s mass. A team of astronomers want to create a catalog of quasar-lenses that will allow them to determine masses for a statistically significant number of quasar host galaxies and to compare them with galaxies without quasars.