My Dark Sky

These two beautiful and almost identical spiral galaxies in Virgo, imaged by the Gemini South telescope in Chile, are NGC5427 (the faced-on spiral galaxy at lower left) and its twin NGC 5426 (upper right). Together, they are known as Arp 271, named after Halton Arp.

Halton Arp is an American astronomer who had catalogues quite a numbers of unusual or peculiar galaxies titled Atlas of Peculiar Galaxies, which almost all of them later turned out to be interacting and merging galaxies, which is quite common in our universe.

At a glance, the galaxies above appear undisturbed and the spiral arms are still intact and distinct. However, mutual gravitational interaction has already begun to alter and distort their visible features. Take another closer look and you will see a bridge of material connecting the two galaxies. This is a tell-tale sign of gravitational interaction between them.

Another sign of interaction between the galaxies is the pinkish knots that trace out the spiral arms in each galaxy. These are the star-forming regions. Where two galaxies gravitationally interacting, the disturbance causes the gases in them collide. This in turn causes the gases to compressed and collapsed to form stars, but not one or two stars, but a whole lot of them – bursts of star formation, or sometime is referred to as starbursts.

Although star-forming regions are common in many spiral galaxies, the ones in Arp 271 are forming at a higher rate, and more plentiful, than expected. Starburst activity can also be seen across the galaxy’s 60,000 light-years connecting bridge.

Arp 271 now is only at their beginning of a violent encounter that will take 100 million years to complete. Over millions of years, the twin galaxies will pass each other, pull back, tangle again… this repeats several times, and finally they will end up as a large and featureless elliptical galaxy, leaving no sign that once upon a time they were a pair of beautiful spiral (except in our pictures on Earth, if we are still around…).

One last thought: The galaxies are 90 million light-years away from us, meaning that the image above was what they looked like 90 million years ago. Today, as we are admiring their beautiful spiral structures in the picture, in reality they may be so distorted that what was left is only a mess, gradually settling down to become an elliptical galaxy.

Source: Gemini Observatory

~ by thChieh on June 27, 2008.

Posted in Galaxies
Tags: Gemini Telescope