I Blame Gravity
Take a look at the galaxies in this image. The one on the left, called NGC 3169, looks a little unsettled, not quite perfectly formed. The one on the right (NGC 3166) seems more blobby and its spiral arms aren’t quite as well-defined as, say, our Milky Way’s.
The reason they look this way?
Gravity. Both galaxies each have an extremely strong gravitational pull, and that plays a part in the cosmic dance they are undergoing.
As each galaxy feels the gravitational influence of the other, a push-pull tug-of-war is warping the spiral shape of one galaxy while fragmenting dust lanes in the other.
Spiral galaxies like NGC 3169 and NGC 3166 usually have arms of stars and dust that are arranged in a swirl around their central regions. They stay in such configurations for quite a long time, until they have close encounters with other galaxies.
When galactic interactions happen, the combined gravity of the objects jumbles things up. The classic spiral shape is stretched and pulled and sometimes torn apart, particularly when the galaxies merge. That’s what gravity does when massive systems of stars get close to each other during their mutual, lengthy cosmic dances.
Unlike the two galaxies shown in the Hubble image above, NGC 3169 and NGC 3166 aren’t yet in a full-out merger. Their close passage toward each other has only begun the transformation they may ultimately undergo. NGC 3169’s arms, shining bright with big, young, blue stars, have been teased apart, and lots of luminous gas has been drawn out from its disc. In NGC 3166’s case, the dust lanes that also usually outline spiral arms are in disarray. Unlike its bluer counterpart, NGC 3166 is not forming many new stars. In a few million years, these two galaxies could look very, very different — and, when their merger (if they have one) is complete, there’ll be an elliptical galaxy left where two majestic spirals once existed. That’s what gravity will do to large-scale stellar systems! For more information on this gorgeous image, visit the ESO web site writeup. There’s way more to these galaxies than meets the casual glance.