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Scientists see signs of ‘fossil galaxy’ lurking in the heart of the Milky Way



This picture shows the Milky Way seen from Earth. The reddish rings highlight where the stars of Heracles dwell in our galaxy.

Danny Horta-Darrington (Liverpool John Moores University), ESA / Gaia and SDSS

Our very own Milky Way galaxy had a dramatic childhood. Astronomers have unveiled a new chapter in his memoir with the discovery of a probable “fossil galaxy”

; hidden near his heart.

The proposed fossil galaxy is called Heracles for the Greek hero. It probably flowed with the Milky Way about 10 billion years ago when our galaxy was baby.

“Stars originally belonging to Heracles account for about a third of the mass of the entire Milky Way halo today – meaning that this newly discovered ancient collision must have been an important event in our galaxy history,” Sloan Digital Sky Survey ( SDSS) said in a statement Thursday. SDSS was involved in the research.

This illustration shows how Heracles fits into the heart of the Milky Way if viewed from above. The yellow dot points out our sun.

Danny Horta-Darrington (Liverpool John Moores University), NASA / JPL-Caltech and SDSS

A research team led by Liverpool John Moore University (LJMU) graduate student Danny Horta published a week on Heracles this week in the Monthly Notices of the Royal Astronomical Society journal.

To find Heracles, the team saw stars that did not match the Milky Way. “These stars are so different that they could only have come from another galaxy. By studying them in detail, we were able to trace the exact location and history of this fossil galaxy,” Horta said.

We have seen signs of dramatic galactic mergers in the Milky Way’s deep past. Recent studies have looked into a time when our galaxy swallowed up a dwarf galaxy called Gaia-Enceladus.

Heracles has been particularly elusive, as evidence of its existence is obscured by interstellar dust clouds. The research team used the SDSS Apache Point Observatory Galactic Evolution Experiment (APOGEE) to look through this mess using near-infrared light. “To find a fossil galaxy like this, we had to look at the detailed chemical composition and motions of tens of thousands of stars,” said co-author of the study and LJMU astrophysicist Ricardo Schiavon.

The Milky Way may not be finished with its galaxy-colliding ways. ONE Milky Way-Andromeda galaxy crash lurking billions of years into the future. It’s hard to be a galaxy. Sometimes you are the Milky Way, eat them up. Sometimes you are Heracles, the one who is swallowed up.


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