The Milky Way Ate One of Its Neighbors 10 Billion Years Ago
Star data shows we gobbled up a galaxy called Gaia-Enceladus about 1/4 the size of the Milky Way, leaving behind telltale signs of the merger
The Milky Way ( NASA/JPL-Caltech/R. Hurt (SSC/Caltech) )
By Jason Daley
smithsonian.com
November 2, 2018 1:45PM
New research suggests about 10 billion years ago the Milky Way consumed a smaller galaxy, and the remnants of that cosmic lunch are still swirling around in the Milky Way’s belly.
The long-ago feast was discovered when researchers looked at data collected by the European Space Agency's Gaia space telescope, analyzing data on tens of thousands of stars within 33,000 light years of our own sun, reports Lisa Grossman at ScienceNews. What the data shows is that a group of about 30,000 of those stars aren’t rotating around the galactic center like they should. Instead, they appear to be moving the opposite way.
“That was the first hint,” astronomer Amina Helmi of the University of Groningen in the Netherlands tells Grossman. “When stars move the opposite way, that already tells you that they basically didn’t form in the same place as the majority of the stars in our galaxy.”
Using the Apache Point Observatory Galactic Evolution Experiment in New Mexico, Amina and her colleagues performed a follow-up, looking at the elements making up the stars. The chemical composition showed that the backward moving stars do not contain the same heavy elements as stars like our own. Instead, they appear to be much older, forming before the cycle of birth and death of massive stars spread heavier elements across the universe, according to a new study published in the journal Nature.
Read more: https://www.smithsonianmag.com/smart-news/milky-way-ate-one-its-friends-10-billion-years-ago-180970696/#x6TkPr7oPYeZbsef.99
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