Did you know that the Milky Way is a cannibal?  I didn’t either.  But, apparently our galaxy has cannibalized a number of galaxies over the course of its life.  Most of those galaxies are smallish and still live within ours.  But, scientists recently found one that didn’t survive being consumed.  And they had help from Gaia herself.

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The European Space Agency’s (ESA) Gaia spacecraft is mapping the location of 1 billion stars in the Milky Way as we speak.  And, it’s doing it with incredible accuracy.  Because Gaia is doing such a bang-up job, scientists were recently able to identify a “set of about 33,000 of those stars that are moving in a completely different manner compared to the bulk of the Milky Way.”  

Research leader Amina Helmi, an astronomer at the University of Groningen in the Netherlands told space.com, “When you look at how stars move, they actually retain in their motions [a] memory of the place where they were born,”.  So, when the research team studied the chemistry of 600 of the stars that were moving in an odd way, they could see that they were born somewhere else, as well as the age and size of the foreign galaxy corpse.  

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Scientists estimate that the dead galaxy “fell” into the Milky Way around 10 billion years ago, and was “likely the last major overhaul to our home galaxy during its development.”  This galaxy made a big impact indeed.  Researchers think that it was about a fifth of the size of our current Milky Way, and that it seeded stars into the inner ring.  That could be an explanation for the density of our galaxy’s disc.  That is yet to be confirmed, but it’s clear that this galactic skeleton floating around in the Milky Way’s belly is a very big deal.   Being able to see it in such detail is an even bigger one.  Praise Gaia.  


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