Gemini South shoots Twin Galaxies NGC 5426-27 aka Arp 271

Click on the image for full resolution

In what appears to be a masterful illusion, astronomers at Gemini Observatory have imaged NGC 5426-27 (Arp 271), two nearly identical spiral galaxies in Virgo, 90 million light years distant, in the early stages of a gentle gravitational embrace. This image was obtained at the Gemini South telescope in Chile using GMOS, the Gemini Multi-Object Spectrograph. Like two skaters grabbing hands while passing, NGC 5427 (the nearly open-faced spiral galaxy at lower left) and its southern twin NGC 5426 (the more oblique galaxy at upper right), are in the throes of a slow but disturbing interaction - one that could take a hundred million years to complete. At a glance, these twin galaxies - which have similar masses, structures, and shapes and are together known as Arp 271 - appear undisturbed. But recent studies have shown that the mutual pull of gravity has already begun to alter and distort their visible features. Typically, the first sign of a galaxy interaction is the formation of a bridge-like feature. Indeed, the two spiral arms on the western (upper) side of NGC 5426 appear as long appendages that connect with NGC 5427. This intergalactic bridge acts like a feeding tube, allowing the twins to share gas and dust with one other across the 60,000 light years (less than one galaxy diameter) of space separating them. Colliding gases caused by the interaction may have also triggered bursts of star formation (starbursts) in each galaxy. Star-forming, or HII, regions appear as hot pink knots that trace out the spiral patterns in each galaxy. HII regions are common to many spiral systems, but the giant ones in NGC 5426 are curiously knotted and more abundant on the side of the galaxy closest to NGC 5427. Starburst activity can also be seen in the galaxy's connecting bridge. Likewise, the giant HII regions in NGC 5427's disk are forming at a higher rate, and are more plentiful, than expected for a galaxy of this type. One giant star-forming region at the tip of NGC 5427's western (top) spiral arm, looks especially large and disturbed, as does the arm itself, which is unusually straight, as if strong tidal forces have broken the arm in two, causing it to bleed starlight. Despite their appearance in this two-dimensional image, NGC 5426's western (top) spiral arm is the one closest to us, as opposed to NGC 5427's southeastern (bottom) arm. NGC 5426 is also the closer of the two galaxies. Over millions of years, however, NGC 5427 will perform a parabolic traverse, moving it from behind NGC 5426 towards the foreground in the upper-right corner of the frame. Thus, an imaginary long-lived observer on a planet in NGC 5427 would see an almost perpendicular passage of the companion galaxy.
Credit: Gemini Observatory