Hubble captures two spectacular views of colliding galaxies

Hubble is doing a series of incredible photos on galaxy collisions, and I want to break a couple of them down for you.

Galaxy collisions take millions and millions of years to occur. It’s not this huge clash that occurs instantaneously. Most of what’s in galaxies is just empty space, plus these collisions take place across such extended timespans, which means that galaxy mergers are actually much less violent than you’d think. Stars and planets aren’t crashing into one another.

Let’s start with a pair of galaxies collectively known as ARP 300, or UGC 05028, which is the smaller galaxy, and UGC 05029, the larger galaxy. They look far away from each other in this photo, but they’re actually in the process of colliding — they’re locked in a gravitational dance with each other right now and eventually they’ll start to merge.

You can see that happening on a smaller scale in UGC 05028. Do you see the secondary bulge in this galaxy? Scientists think that’s likely the result of a previous collision, and that the two galaxies have almost completed their merger. Eventually UGC 05028 will look seamless, like the larger galaxy.

See the bright blue dots in the outer arms of both galaxies? This is where rapid star formation is happening, thanks to the galaxy merger. When this type of interaction happens, the gas and dust within the galaxies becomes compressed and that can trigger huge bursts of star formation. That’s probably what’s happening here.

Let’s move onto the next photo.

Here you can see four distinct spiral galaxies. The largest, on the left, is NGC 1356. LEDA 467699 is above it, LEDA 95415 is to the left of it, and finally IC 1947 is way off on the left of the image.

(If you’re wondering where these names come from. These are just different ways of cataloging deep space objects — NGC is New General Catalog of Nebulae and Clusters, and it was first compiled in 1888. IC is the index catalog, which was added in 1895, and both have been added to over the centuries. LEDA was started in 1983 and is continually updated, most galaxies have a LEDA identification in addition to their other name.)

Ok, back to the photo: It’s a great lesson in perspectives, which is very hard to tell in a photo like this. For example, it looks like these two galaxies, NGC 1356 and LEDA 95415, are on the brink of merging with one another. In reality, they’re about 300 million light years away from one another. In contrast our neighboring galaxy Andromeda is 2.5 million light years away from us. If you' want to know distance from Earth, the large galaxy in this photo NGC 1356 is about 550 million light years away from us.

One way you can tell that these two aren’t actually colliding in the photo is that they still have their distinct shapes and NGC 1356 still has a nice glowy trail here in its outer arm that isn’t interrupted by the seemingly smaller galaxy. If they were interacting at the level that’s implied by this photo, they wouldn’t have their nice spiral shapes anymore.

If you’re wondering which galaxies in this image are really interacting, it’s the two that look furthest from one another: NGC 1356 and IC 1947. They’re just 400,000 light years away from each other.

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