Astronomers Find Cosmic Lenses with Feeding Black Holes

The Hubble Space Telescope's sharp view was used to look for gravitational arcs and rings (indicated by arrows), which are produced when one galaxy acts as a lens to magnify and distort the appearance of another galaxy behind it. In this case, the foreground galaxies contain actively accreting black holes called quasars. Image credit: NASA, ESA, EPFL (Switzerland)


In space, it sometimes happens that two galaxies are aligned in just the right way that the closer galaxy distorts and magnifies the appearance of the one behind it. For astronomers, finding these alignments is like coming across giant, cosmic magnifying glasses. 

Now, a team of astronomers, including Daniel Stern from NASA's Jet Propulsion Laboratory in Pasadena, Calif., has found several rare examples of this phenomenon, called gravitational lensing, in which the foreground galaxy hosts an actively accreting supermassive black hole. 

Such feeding black holes, called quasars, are among the brightest objects in the universe, far outshining the total starlight of their host galaxies. Because they are so bright, it is hard for astronomers to measure the mass of their host galaxies. However, gravitational lenses are invaluable for estimating the mass of a quasar's host galaxy. The amount of the background galaxy's distortion can be used to accurately measure the lensing galaxy's mass. 

The team hopes to build an even bigger catalog of these quasar lenses, and to use these data to better understand the interplay between black hole feeding and star formation in galaxy evolution.