In more than 13 billion years of its history, the Galaxy has experienced many mergers and acquisitions with large and small neighbors. Ricardo Schiavon and his colleagues discovered traces of one of the first such events in the APOGEE experiment: the remains of an ancient galaxy that died 10 billion years ago but remained in the Milky Way. The scientists ‘ article was published in the journal Monthly Notices of the Royal Astronomical Society, Naked Science.
“To find such remnants of a galaxy, you need to know the exact composition and motion parameters of tens of thousands of stars,” Ricardo Schiavon says. — This is especially difficult for stars located in the direction of the center of the Milky Way, where dense dust clouds interfere.” Therefore, during the APOGEE experiment, which lasted a whole decade, more than half a million stars were observed in the near-infrared range, which allows you to look through the dust.
Among all these stars, scientists have identified a population that differs from the rest in speed and low metallicity. The content of elements is heavier than hydrogen and helium. By tracking their movements, the study authors were able to reconstruct the past of the galaxy they once represented. It was given the name Heracles.
Unlike most other remains of other galaxies found in the Milky Way, these are located not on the rarefied halo’s outskirts, but in its inner regions, within four-kilo parsecs from the center of the Galaxy. Scientists attribute this to the fact that Hercules was absorbed in the early stages of the Milky Way when it did not reach its current size and mass.
According to researchers, this happened 10 billion years ago, and Hercules’ mass was then about 500 million times the Sun’s mass. Today, the remaining stars may account for up to a third of the total population of the Milky Way halo.