Our Milky Way galaxy is going to collide with the Andromeda Galaxy. There’s no need to panic — it won’t happen for several billion years — but astronomers do want to know what things will look like once the galaxies merge. Luckily, astronomers just found a bunch of merging galaxies that will better help them predict what will happen when the big collision finally comes to our neighborhood.
Caught in the Act
Galaxy mergers are really common. In fact, the Milky Way probably swallowed some smaller galaxies over its long history. But at the center of many galaxies sits a giant black hole, and what really makes mergers interesting is how those behave in the process. Since black holes have huge gravitational fields, it’s fun to watch what happens when you put two ginormous ones next to each other.
For the study, which was published in Nature, the astronomy team looked at dozens of nearby galaxies using NASA’s Hubble Space Telescope and Hawaii’s W.M. Keck Telescope. From that dataset, the team spotted about 20 galaxies undergoing mergers. The lead author said observing these galactic pairs is “pretty amazing.”
“In our study, we see two galaxy nuclei right when the images were taken. You can’t argue with it,” said lead author Michael Koss, a research scientist at Eureka Scientific Inc., in a press release from the University of Maryland (where he got his Ph.D.) “It’s a very clean result, which doesn’t rely on interpretation.”
More Than Meets the Eye
This study is unique because it managed to capture black holes in a late stage of the merger process when they’re obscured in gas and dust and difficult to see. Previous studies saw the collisions, but only when the individual black holes were about 10 times further away.
The key to success here lay in using both the Hubble and Keck telescopes. Hubble’s X-ray data pointed the way to merging galaxies, and then Keck’s infrared eyes were able to see through the dust and gas blocking the view.
The results really surprised astronomers. Of the nearly 500 galaxies surveyed, roughly 17 percent of them had merging black holes in their centers. Astronomers used to think the latest stages of merger would be nearly impossible to see because simulations suggested the merger would take relatively little time (at least in galactic terms — in terms of human lifespans, not so much.)
To really get a good look, however, astronomers are eagerly awaiting the launch of NASA’s James Webb Space Telescope. The much-delayed observatory is now set for launch in 2021. When it finally gets to space, astronomers think it will show a much better view of merging galaxies with its infrared cameras. The telescope can even measure the mass and growth rates of the black holes that are closest to it.
“With these observations, we can begin to explore the fraction of objects that are merging in the youngest, most distant regions of the universe — which should be fairly frequent,” said study co-author Sylvain Veilleux, an astronomy researcher at the University of Maryland, in the same statement. The future is looking bright — if a little messy.