That Hubble Went out to Play
And what a time it’s been! As you can see by this image, the most famous of the Great Observatories is still crankin’ out some stunning visions of the cosmos. Take this image, for example. It’s a pair of interacting galaxies, slightly farther along in their gravitational dance than the two I wrote about in my last entry. They are an interesting looking grouping called Arp 273.
The larger of the spiral galaxies in the group, known as UGC 1810, has a disk that is distorted into a rose-like shape by the gravitational tidal pull of the companion galaxy below it, known as UGC 1813. Not only are these two cosmic behemoths changing each other’s shapes, but in the process, they’re spurring huge swaths of star-forming factories in the process. Those are the blublogs at the top of UGC 1810, and the bluish clouds of light at the tip of the lower galaxy. The image (embiggenate to see it better) shows a tenuous tidal bridge of material between the two galaxies that are separated by tens of thousands of light-years from each other.
Even more unusual are the off-center spiral patterns of each galaxy. Even if you didn’t know anything else about these galaxies, just one look at the off-kilter spirals would tell you that something has happened. In this case, one galaxy has dived through the center of the other. The smaller one probably sliced right through its larger companion above it in this image.
Notice how the spiral arms of UGC 1810 (the upper one) are warped off-kilter with respect to each other. The inner set is offset out of the plane of the galaxy. This must have been a titanic interaction!
As if this wasn’t weird enough, there’s also a possible mini-spiral in the upper right arms of UGC 1810.
Astronomers have seen many interacting galaxies — enough to be able to understand something of how and why they form. In this case, the larger galaxy of the pair is about five times more massive than its smaller companion. In unequal pairs such as this, the relatively rapid passage of a companion galaxy produces the lopsided or asymmetric structure in the main spiral. Also in such encounters, the starburst activity typically begins in the minor galaxy earlier than it does in the major galaxie. These effects could be due to the fact that the smaller galaxies have consumed less of the gas present in their nucleus — and that gas is what you need for stars to form. The gravitational shock waves spur “bursts” of star formation as the gas is compressed and heated during the interaction.
Arp 273 lies in the constellation Andromeda and is roughly 300 million light-years away from Earth. This image is just one of a stream of cosmic visions sent back by Hubble during its 21 years on orbit. Currently, the telescope is in great shape and should continue its work for some time to come.
