Astronomers using two 10-m optical/infrared telescopes at the W. M. Keck Observatory have discovered the first quadruple quasar, catalogued as SDSS J0841+3921. This image shows the quadruple quasar SDSS J0841+3921 (quasars are indicated by arrows). Image credit: Joseph Hennawi / Fabrizio Arrigoni-Battaia. The quartet – four active black holes situated in close proximity to one another – resides in one of the most massive structures ever...
