The first time I saw an image of the Antenna Galaxies, I knew I had to image them. I know it had to be some variant of “wow” or “whoa” that escaped my lips. They are an amazing thing to see. These aren’t some stately, grand-designed spiral galaxies moving serenely through the cosmos. They’re messy. But in that mess, you can see gravity in action, and that has its own beauty. And perhaps we’re getting a look at our own future when the Milky Way and Andromeda galaxies begin to merge in a few billion years.

These are southern galaxies in the constellation Corvus. They’re at a declination of minus 18 degrees, and that means they never get very high for me at my latitude of 39 degrees north. They transit the meridian at only around 31 degrees up in the sky, and that’s their highest point, so imaging time is relatively limited.

I actually imaged this using a telescope at Sierra Remote Observatories in California, but that’s at about the same latitude. Because it never gets very high in the sky, that means that we’re always imaging through a lot of atmosphere, which is a little detrimental to the final image quality. But southern observers are better situated as it gets higher in the sky for them. For those in higher northern latitudes, this may never get high enough to really see well at all.

Most northerners who aren’t interested in astronomy have never even heard of Corvus. Corvus means “crow” in Latin, and I don’t know how anyone sees a crow shape in those stars, but perhaps ancient peoples had a better imagination than I do. It’s a small constellation, and its brighter stars are dimmer than Polaris. So if you have trouble seeing Polaris, then the stars of Corvus are going to be even more challenging, especially if it’s low on your horizon.

The pair of galaxies making up the Antennae Galaxies have multiple names. They’re known as NGC 4038 and 4039, and also Caldwell 60 and 61. They were discovered by William Herschel in 1785, and they’ve been the subject of numerous astronomical studies since then, trying to understand the nature of interacting galaxies.

They’re thought to be about 45 million light years away. When you first see the galaxies, the feature that jumps out to most are the “antennae” that give the pair of galaxies their name. These antennae are long tidal tails of stars that have been stretched out through the gravitational interaction of the two galaxies. If there’s anybody living on planets in those tidal tails, they must have a spectacular view of the main disks of the galaxies overhead in the night sky!

Also, because of that gravitational interaction, these are starburst galaxies. A typical galaxy like our own produces stars at a rate of about three solar masses per year. In a starburst galaxy, that rate can be over a hundred solar masses worth of stars per year. Because of this, the reservoirs of slow-moving gas will be consumed much more quickly, and so star formation will come to an end much more quickly than if these galaxies had never met. The results of all that star formation can be seen in the hot blue regions in the merging galaxy. That indicates the presence of many hot, young, blue stars. But there are also large red patches of nebulosity, so these galaxies haven’t used up all their hydrogen yet.

According to Wikipedia, the Antennae Galaxies are home to relatively young globular clusters. Most galaxies have a smattering of globulars around them, and those globulars are old, around 12 billion years old. But these are much younger, thought to be the result of the merger process. In this case, that puts them at an age of no more than about half a billion years, since scientists think the merger process started happening after that point. I’m speculating that means the globulars have much younger stars in them, but the article isn’t clear on how that age was determined.

Again, according to Wikipedia, around 1.2 billion years ago, NGC 4038 was a barred spiral galaxy, and NGC 4039 was a spiral galaxy, one without a bar. Around 900 million years ago, they began to approach one another. About 300 billion years ago, the antennae began to form. Within 400 million years from now, the nuclei of the two galaxies will merge, and the result should be an elliptical galaxy.

Interacting galaxies are one of the most amazing things to see in the sky. They bring a dynamism to subjects that we tend to think of as essentially unchanging. And while we can only see a snapshot of that process, the snapshot does reveal the history and the future of these galaxies all in one image.

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