Siamese twin galaxies in a "gentle gravitational embrace"

Washington, June 27 : Astronomers at Gemini Observatory have imaged two nearly identical spiral galaxies in Virgo, which is 90 million light years away, in the early stages of a gentle gravitational embrace.

The new image was obtained at the Gemini South telescope in Chile using GMOS, the Gemini Multi-Object Spectrograph.

What the image shows is that NGC 5427 and its southern twin NGC 5426 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.

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 regions appear as hot pink knots that trace out the spiral patterns in each galaxy.

Such 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 star forming 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.

Once thought to be unusual and rare, gravitational interactions between galaxies are now known to be quite common (especially in densely populated galaxy clusters) and are considered to play an important role in galaxy evolution.

The new Gemini image is possibly a preview of things to come for our own galaxy. Ultimately, the end result of these types of collisions is thought to result in a large elliptical galaxy.

ANI