Gemini’s galactic twins

Contributed by
Jun 26, 2008

The Gemini South massive 8-meter telescope captured a beautiful moment in a destructive dance.


These two galaxies, individually called NGC 5426 (left) and NGC 5427 (right) are together called Arp 271. Halton Arp is an astronomer who spent quite a bit of time cataloging unusual galaxy systems, and almost all of them turned out to be interacting. In this case, the two magnificent spirals, lying 90 million light years away from Earth, are just starting to collide. Although they look intact, tell-tale signs of their mutual gravitational train-wreck are there: the spiral arms are just starting to distort, and the giant gas clouds (seen as the pinkish blobs) are more common than expected. Also, they appear to be knottier and more abundant on the sides of each galaxy closest to the other galaxy (despite appearances, I think the left side of NGC 5426 is closer to NGC 5427 which is behind the more face-on galaxy; it can be difficult to judge these things in an image though).

This means that the two galaxies are beginning the first steps of a dance that will take 100 million years to complete. They will pass each other, slow, then tangle again. This may happen several times, but in the end they will most likely merge, forming a large, puffy, elliptical galaxy. The fireworks will be spectacular as cloud collisions hugely accelerates star formation, lighting up the gas, causing frequent supernova...

... and also, perhaps, dumping gas into the central black holes no doubt lurking in the hearts of both galaxies. When that happens, the matter will heat up and glow incredibly brightly, turning this mess into an active galaxy. But eventually even that will settle down, and in the end, the signs that the one elliptical was once two stately spirals will be subtle and few.

Don't forget: we're headed toward the Andromeda galaxy as well. In a billion years or two, this will be us. Looking outward sometimes helps us look inward. The fate of the denizens of the universe is sometimes our own, too.

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