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