Astronomers Spot New Stars That Signal Upcoming Galactic Collision

Scientists have long suspected that the Large and Small Magellanic Clouds are on a collision course with our Milky Way galaxy, and it may be running ahead of schedule. While analyzing objects at the edge of the galaxy, astronomers noted an unexpected cluster of young stars. Upon closer examination, these celestial objects may be harbingers of an impending collision between the Milky Way and the Magellanic dwarf galaxies. 

According to Adrian Price-Whelan, a research fellow at the Flatiron Institute’s Center for Computational Astrophysics, there are fewer than a thousand stars in the newly discovered cluster. Nevertheless, this discovery could have significant implications for astronomy. Stars at the edge of the Milky Way are among the oldest in the galaxy, so a group of young stars is notable. 

Until recently, astronomers didn’t have the data to locate and analyze groups of stars like this, but the ESA’s Gaia spacecraft has changed that. This mission has already mapped the positions of more than 1.7 billion stars. It was this data that allowed the team to identify the “Price-Whelan 1” cluster. The image below shows those stars, highlighted in blue. Most of them are around 117 million years old, which is nothing compared with the multi-billion-year-old stars that surround Price-Whelan 1.

The team immediately noted that Price-Whelan 1 sits near a river of gas known as the Magellanic Stream — the outer edge of the Large and Small Magellanic Clouds. Astronomers believe the Magellanic Stream will eventually carry the dwarf galaxies into the Milky Way, but perhaps the Price-Whelan 1 cluster indicates that the process is already underway. David Nidever of Montana State University analyzed the metal content of the cluster, hoping to tie the stars to the Magellanic Stream. The results indicate that, just like the Magellanic Stream, these stars have very low metal content. 

The team speculates that gas from the Magellanic Stream began interacting with the Milky Way over 100 million years ago. The gravity and tidal forces at work in the Milky Way compressed the gas enough to trigger star formation. Those stars were eventually pulled into the galactic disk, where Gaia could measure their position and movement. Using this data, the team has estimated the current edge of the Magellanic Stream is 90,000 light-years from the Milky Way, half as far as previously believed. This data could help us estimate when the collision will occur and what will happen when it does. We may even be able to determine if the Large and Small Magellanic Clouds have passed through the Milky Way before.

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