Scientists have found evidence of a dead galaxy in the Milky Way, which arrived following a collision 10 billion years ago. Researchers have dubbed the deceased galaxy “Heracles” and is thought to be a remnant of the early Universe.
Scientists believe the remnants of the ancient galaxy accounts for roughly a third of the Milky Way’s spherical “halo” – an area made up of star clusters, gases and dust.
Fossil galaxies can be found as they are usually on the edges of the Milky Way.
However, the current one was found deep inside, suggesting it was a galaxy which first came to fruition shortly after the creation of the Universe.
To discover the fossil, the team used data from the Apache Point Observatory Galactic Evolution Experiment (Apogee) project.
Dr Ricardo Schiavon, of Liverpool John Moores University’s Astrophysics Research Institute, said: “To ‘catch sight’ of that galaxy is awesome.
“It is really small in the cosmological context – only 100 million stars – but accounts for almost half the mass of the entire Milky Way halo.
“To find a fossil galaxy like this one, we had to look at the detailed chemical make-up and motions of tens of thousands of stars.
“That is especially hard to do for stars in the centre of the Milky Way, because they are hidden from view by clouds of interstellar dust.
“Apogee lets us pierce through that dust and see deeper into the heart of the Milky Way than ever before.”
To separate which stars belonged to Heracles originally, the team analysed the chemical composition of the stars.
Danny Horta, a graduate student at Liverpool John Moores University, said: “Of the tens of thousands of stars we looked at, a few hundred had strikingly different chemical compositions and velocities.
“These stars are so different that they could only have come from another galaxy.
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“By studying them in detail, we could trace out the precise location and history of this fossil galaxy.”
The team believe that the merger of Heracles “must have been a major event in the history of our galaxy”, according to the research published in the journal The Monthly Notices Of The Royal Astronomical Society.
This would make the Milky Way an oddity as “most similar massive spiral galaxies had much calmer early lives”.
Dr Schiavon said: “As our cosmic home, the Milky Way is already special to us, but this ancient galaxy buried within makes it even more special.”
However, the Milky Way is not done with its mergers.
Andromeda, the Milky Way’s nearest, and much bigger, neighbouring galaxy is headed towards us.
Andromeda is approaching the Milky Way at around five million kilometres a year, and in two to four billion years, it could consume our home galaxy.
However, humanity will not have to worry about that, as our Sun will have destroyed the solar system by that point.
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