There’s A Dwarf Galaxy Hidden Inside the Milky Way
The Milky Way evolved billions and billions of years ago when clouds of cosmic matter coalesced into a halo spheroid that then collapsed into a spinning disk.
At least that’s what happens in the peaceful model of the origins of our galaxy. More recent evidence has revealed that the Milky Way enjoyed a turbulent youth, swallowing up other galaxies to form the vast spiral system we know today. In particular, new research published in Monthly Notices of the Royal Astronomical Society details one of the Milky Way’s potential conquests: a dwarf galaxy whose stellar remnants have become part of ours.
The first stars to emerge after the Big Bang were composed primarily of hydrogen and helium, simple elements that were abundant at the time, and many of these slow-burning stars are still around today. After several billion years of stellar evolution and fusion, stars began to produce heavier elements, such as metals. In fact, the metal content of stars is one way that astronomers can gauge their relative ages.
Read more: “The Myths and Lore of the Milky Way”
After studying the chemical composition of 20 “metal-poor” stars, an international team of astronomers determined that they likely came from another galaxy, which they called “Loki.” Although metal-poor stars are not uncommon in our galaxy’s halo, a spherical area surrounding the spiral, this cluster is found in the galactic disk. Essentially, these metal-poor stars are more embedded in the Milky Way than their ancient chemical compositions suggest.
“These building blocks coalesced in early epochs, dispersing their stellar, gaseous, and dark matter contents throughout the forming proto-galaxy,” the authors wrote. “Therefore, the more metal-poor stars originating from the first galactic assembly are expected to populate the inner regions of the Milky Way, while those accreted later might be scattered in the outer halo.”
Of course, Loki isn’t the only galaxy consumed by the Milky Way. Research published in 2020 reveals that a massive galaxy called “Kraken” merged with ours about 11 billion years ago, one of the most formative experiences for our young galaxy. Since then, things have calmed down a bit, but we could still be on a collision course with the Andromeda Galaxy, our larger neighbor.
We have at least a few billion years to prepare.
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Main image: NASA/JPL-Caltech
