Free Astronomy Magazine September-October 2014

the images of distant galaxies –which, thanks to a natural “lens effect” that en- hances their brightness, can be analyzed, even if their form usually appears distort- ed. While examining a detailed image of SDSS J1531+3414, taken by Hubble in the ultraviolet-visible domain, a group of re- searchers led by Grant Tremblay (European Southern Observatory) discovered almost by chance that two large elliptical galaxies in the central region of the cluster, both about 330,000 light-years wide, are linked together by a chain of compact and very bright bluish structures, that are in turn interconnected by filaments of hydrogen. The overall form vaguely resembles that of a corkscrew, with the galaxies representing its two winged levers. Since SDSS J1531 +3414 is rich of arcs, streaks and bright clumps created by the powerful gravita- tional field that deforms the background galaxies lying on the same line of sight, astronomers had initially speculated that also this unusual chain was a consequence of lensing. In a subsequent verification made by Tremblay’s team with the Nordic Optical Telescope (2.5 metres diameter, Ro- que de los Muchachos Observatory, La Pal- ma, Canary Islands), it was though found that their distance from Earth is quite com- M agnification of the region around SDSS J1531 +3414 occupied by the two large ellip- tical galaxies (yel- low nuclei with or- ange halos), which by coming into collision have trig- gered the forma- tion of the 19 su- perclusters (blue speckles) discov- ered by Tremblay's team. [NASA, ESA/ Hubble, ESO]