A group of young stars at the edge of the Milky Way has signaled to astronomers that a future galaxy collision has started bearing its early fruits. Our galaxy will merge with two smaller ones, the Large and Small Magellanic Clouds, over the next few billion years. And this interaction is already underway.
The research was published in The Astrophysical Journal and presented at the American Astronomical Society meeting in Honolulu on January 8. The cluster is just 117 million years old, very young in star terms, and is located on the outskirts of the Milky Way in a region near the Magellanic Stream, a river of gas stretching from the Magellanic Clouds towards our galaxy.
“It’s really, really far away. It’s further than any known young stars in the Milky Way, which are typically in the disk. So right away, I was like, ‘Holy smokes, what is this?’” primary discoverer Adrian Price-Whelan, from the Flatiron Institute’s Center for Computational Astrophysics, said in a statement. “This is a puny cluster of stars – less than a few thousand in total – but it has big implications beyond its local area of the Milky Way.”
The observations were only possible with the incredible data from the European Space Agency telescope Gaia. Gaia is classifying the position and velocity of 1.7 billion stars. Price-Whelan searched for previously unknown clusters and found just this one. And it was further out than expected.
Together with colleagues, he studied the properties of the cluster and believed it was formed by a little bit of the Magellanic Stream getting compressed in the interaction between the three galaxies. Combining this hypothesis with the motion data from Gaia, the team was able to estimate the distance to the Magellanic Stream, something very difficult to do precisely. They got an answer of 90,000 light-years, half of the previous estimate.
“If the Magellanic Stream is closer, especially the leading arm closest to our galaxy, then it’s likely to be incorporated into the Milky Way sooner than the current model predicts,” said co-author Professor David Nidever from Montana State University. “Eventually, that gas will turn into new stars in the Milky Way’s disk. Right now, our galaxy is using up gas faster than its being replenished. This extra gas coming in will help us replenish that reservoir and make sure that our galaxy continues to thrive and form new stars.”
The work will improve simulations of the future interaction between the galaxies, but the opening salvo has been shot.