Ancient “fossil galaxy” sighted inside our Milky Way – BGR

• Scientists have discovered the remains of an ancient “fossil galaxy” hidden within our Milky Way.
• The galaxy is what remains of a very ancient galaxy that collided with our galaxy a long time ago, scientists think.
• The galaxy was identified by spotting old stars with a different makeup in the depths of the Milky Way.

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Understanding how galaxies are born, grow and die is essential to better understanding how the universe itself works. As for our Milky Way, we know quite a lot, but not enough to say for sure how it formed, and certainly not enough to know how long it took to reach its current state.

Now, researchers using data from the Sloan Digital Sky Survey’s Apache Point Observatory Galactic Evolution Experiment (wow, that’s just a mouthful) say they have discovered the remains of an ancient “fossil galaxy” that may have contributed greatly to the growth of the Milky Way.

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The fossil galaxy – which scientists have dubbed “Hercules” – is actually quite substantial in terms of the overall size of the Milky Way. Researchers believe it makes up “about one third of the spherical halo of the Milky Way”. This is a huge portion of our home galaxy, and no one has ever seen it before due to how close it is to the center of the galaxy. The study was published in Royal Astronomical Society Monthly Notices.

“To find a fossil galaxy like this, we had to examine the detailed chemical composition and motions of tens of thousands of stars,” Ricardo Schiavon, co-author of the research, said in a statement. “This is particularly difficult for stars at the center of the Milky Way to do, because they are hidden from view by clouds of interstellar dust. APOGEE allows us to penetrate through that dust and see deeper into the heart of the Milky Way than ever. “

Using APOGEE to study an astonishing number of stars and then compare their composition, the researchers were able to spot a stark difference between the vast majority of stars and a collection of “a few hundred” that were very clearly different.

“Of the tens of thousands of stars we observed, a few hundred had strikingly different chemical compositions and speeds,” explained lead author Danny Horta. “These stars are so different that they could only come from another galaxy. By studying them in detail, we could trace the exact location and history of this fossil galaxy. “

So how did this ancient galaxy become part of ours? Scientists suggest it is possible that the galaxy collided with our Milky Way very early in its formation. When that happened, it would have greatly strengthened the size of our galaxy and could be at least partly responsible for the health of the Milky Way today.