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The ‘fossil galaxy’ discovered deep in the Milky Way is the remnant of a star cluster that collided with our own 10 BILLION years ago and was absorbed into its ‘halo’, astronomers say
- Experts have analyzed the composition and movement of tens of thousands of stars
- This allowed them to identify the hidden remnants of the galactic collision
- The “fossil” – located near the center of the Milky Way – has been nicknamed Heracles
- Large galaxies are formed through the process of such collisions and mergers
Another galaxy was absorbed into ours after a collision with the Milky Way about 10 billion years ago, astronomers revealed.
Liverpool experts have discovered this galactic “fossil” hidden deep in the Milky Way by analyzing the movements and composition of tens of thousands of stars.
This cosmic remnant, nicknamed “Heracles” by the hero of ancient Greek mythology, represents one third of the spherical halo of stars and gas of the Milky Way.
The remnants of a number of old galaxies had already been identified in the outer halo of the Milky Way – indeed, it is through mergers that large galaxies are formed.
However, to find such early mergers requires analysis of the most central part of the Milky Way halo, such that it is buried deep in the galaxy’s disk and bulge.
Another galaxy was absorbed into ours after a collision with the Milky Way about 10 billion years ago, astronomers revealed. In the photo, an artist’s impression of the Milky Way as it could be seen from above. The red rings represent the position of the fossil galaxy
“Seeing that galaxy is fantastic,” said author and astrophysicist Ricardo Schiavon of Liverpool John Moores University.
“It’s really small in the cosmological context – only 100 million stars – but it accounts for nearly half the mass of the entire Milky Way halo.”
In their study, Dr. Schiavon and colleagues analyzed data collected by the Apache Point Observatory Galactic Evolution Experiment, or “APOGEE” project, which collected data on more than half a million stars across the Milky Way.
‘To find a fossil galaxy like this, we had to look at the detailed chemical composition and movements of tens of thousands of stars,’ explained Dr. Schiavon.
“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.”
Liverpool experts have discovered this galactic “fossil” hidden deep in the Milky Way by analyzing the movements and composition of tens of thousands of stars. This cosmic remnant, nicknamed “Heracles” by the hero of ancient Greek mythology, represents one third of the spherical halo of stars and gas of the Milky Way. In the photo, the position of Heracles as seen through the plane of the Milky Way
“Of the tens of thousands of stars we observed, a few hundred had surprisingly different chemical compositions and speeds,” said article author Danny Horta, also of Liverpool John Moores.
“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,’ he explained.
Based on their findings, the team concluded that the collision between Heracles and the Milky Way “must have been a major event in the history of our galaxy.”
This, they added, makes the Milky Way unusual among its kind, as “most similar massive spiral galaxies have had much quieter lives.”
“As our cosmic home, the Milky Way is already special to us, but this ancient galaxy buried within it makes it even more special,” concluded Dr. Schiavon.
The full study results were published in The Monthly Notice of The Royal Astronomical Society.
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