This Strange-Looking Galaxy is Actually Two. And They're Merging

By Nancy Atkinson January 19, 2024
This Strange-Looking Galaxy is Actually Two. And They're Merging

This strange-looking galaxy seems to be a spiral with a long tidal tail stretching away. It's known as Arp 122, and it's actually not just one galaxy, but two separate galaxies. NGC 6040 is the warped spiral galaxy seen edge-on, while LEDA 59642 is the round, face-on spiral. The two are colliding about 540 million light-years from Earth, and it gives us a preview of the Milky Way's future collision with Andromeda.

This image was taken by the venerable Hubble Space Telescope

What will Arp 122 look like when the merger is complete? We’ll try to keep you posted, but this ongoing merger will take hundreds of millions of years, so be patient.

While galactic mergers incredibly dramatic and energetic events, they occur at a snail’s pace, just because of the massive distances involved. But still, even a slow-motion collision can create chaos and grandeur. Star formation begins to ramp up from collisions of gas clouds and extreme gravitational interactions. Usually, the merged galaxies can shine up to ten times brighter than they did individually. Over time, this completely changes the structure of the two (or more) colliding galaxies, usually results in a single, merged galaxy.

The Mice Galaxies (NGC 4676) are famous interacting galaxies currently undergoing a process of collision and merger. The long tail on the right side is a result of the gravitational tidal forces during the merging process. When galaxies merge, a significant amount of molecular gas flows into the central region, promoting the formation of numerous stars and facilitating the growth of supermassive black holes. Image Credit: NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA.

The collisions can also create stellar features called tidal tails, like the one seen in Arp 122, or in the Mice Galaxies, above. The tails can look like streams or arcing rivers of stars moving along in the wake of the collision. Other features can be created that look like ripples, similar to how ripples form when you toss a rock into a pond. Astronomers have learned how to interpret the different features to learn more about the original galaxies and their collisions.  

And don’t worry about the Milky Way’s collision with its nearest galactic neighbor, the Andromeda Galaxy (M31). We have at least four billion years to wait before they actually meet up.

Nancy Atkinson

Nancy Atkinson

Nancy Atkinson is a space journalist and author with a passion for telling the stories of people involved in space exploration and astronomy. She is currently retired from daily writing, but worked at Universe Today for 20 years as a writer and editor. She also contributed articles to The Planetary Society, Ad Astra (National Space Society), New Scientist and many other online outlets.

Her 2019 book, "Eight Years to the Moon: The History of the Apollo Missions,” shares the untold stories of engineers and scientists who worked behind the scenes to make the Apollo program so successful, despite the daunting odds against it. Her first book “Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos” (2016) tells the stories of 37 scientists and engineers that work on several current NASA robotic missions to explore the solar system and beyond.

Nancy is also a NASA/JPL Solar System Ambassador, and through this program, she has the opportunity to share her passion of space and astronomy with children and adults through presentations and programs. Nancy's personal website is nancyatkinson.com