ABELL

1689

Sky at Night Magazine - - THE VIRGO GALAXIES -

As­tron­omy is full of mind-bend­ing physics – and there’s no short­age of weird and won­der­ful be­hav­iour in and around gal­ax­ies. Nowhere is this bet­ter demon­strated than when dis­tant gal­ax­ies swarm to­gether in vast clus­ters. Abell 1689 is one such galaxy clus­ter that as­tronomers have scru­ti­nised in­tensely in re­cent decades. It lies at the heart of Virgo, around 7.5° east of the bright star Por­rima (Gamma Vir­gi­nis). At a dis­tance of over two bil­lion lightyears from us, and ex­tremely faint, this clus­ter is not one you’ll be track­ing down through the eyepiece of a mod­est back-gar­den tele­scope. But thanks to the pow­er­ful or­bit­ing eye of the Hub­ble Space Tele­scope, this far­away ga­lac­tic gath­er­ing has been imaged in spec­tac­u­lar de­tail re­veal­ing a lot more than just the in­di­vid­ual glow­ing mem­bers of the clus­ter it­self.

Scan your eyes over Hub­ble’s im­age of Abell 1689 (right) and you might see what makes the clus­ter so in­ter­est­ing. Scat­tered through­out it are thin, hair-like arcs of light. These aren’t ex­otic ce­les­tial struc­tures, but highly warped vi­sions of other gal­ax­ies that sit far beyond the clus­ter. These arcs ap­pear be­cause the huge com­bined mass of the clus­ter gal­ax­ies dis­torts the space sur­round­ing it, caus­ing it to be­have like a lens. Though the qual­ity of the im­age pro­vided by this grav­i­ta­tional lens might raise eye­brows in am­a­teur tele­scope-mak­ing cir­cles, the lens shares one key trait with the tele­scope lenses we use: it can re­veal dis­tant ob­jects that we might oth­er­wise be un­able to see. In­deed in 2008 re­searchers an­nounced that they’d used Hub­ble, in con­junc­tion with the Abell 1689’s grav­i­ta­tional lens, to ob­serve a dis­tant galaxy in the early Uni­verse, some 700 mil­lion years af­ter the Big Bang.>

The blue, hair-like arcs in this im­age are gal­ax­ies beyond Abell 1689 made vis­i­ble by grav­i­ta­tional lens­ing

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