Free Astronomy Magazine September-October 2014

47 GALAXIES SEPTEMBER-OCTOBER 2014 nary stellar T he interaction between galaxies is a fundamental process in the evolution of the universe and it is often the ori- gin of very spectacular and sometimes un- expected structures. It is the case of a clus- ter of galaxies known as SDSS J1531+3414 (since catalogued for the first time in the Sloan Digital Sky Survey), lying on the bor- T he centre of SDSS J1531 +3414, dominated by the pair of ellip- tical galaxies asso- ciated with stellar superclusters. [NA- SA, ESA/Hubble, G. Tremblay/ESO] der between the constellations of the Co- rona Borealis and Bootes, distant about 3.7 billion light-years, and with a mass in ex- cess of about 4,000 Milky Way masses. This cluster is one of 23 included in the Hubble Space Telescope observing program, whose purpose is to investigate in detail the ef- fects produced by gravitational lensing in