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The “ fossil galaxy ” discovered deep in the Milky Way is the remnant of a star cluster that collided with ours 10 billion years ago and was absorbed into its “ halo say astronomers
- Experts have analyzed the composition and motion of tens of thousands of stars
- This allowed them to identify the hidden remnant of the galactic collision.
- The ‘fossil’ – located near the center of the Milky Way – has been dubbed Heracles
- Large galaxies are built through the process of such collisions and mergers
Another galaxy was absorbed into ours after colliding with the Milky Way around 10 billion years ago, astronomers have revealed.
Experts in Liverpool 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”, after the hero of ancient Greek mythology – represents a third of the spherical “halo” of stars and gas in the Milky Way.
The remains of a number of ancient galaxies had previously been spotted in the Milky Way’s outer halo – in fact, it’s through mergers that large galaxies are built.
However, to find these early mergers, one must analyze the most central part of the Milky Way’s halo – as it is buried deep within the disk and bulge of the galaxy.
Another galaxy was absorbed into ours after colliding with the Milky Way around 10 billion years ago, astronomers have revealed. Pictured is an artist’s impression of the Milky Way as it could be seen from above. The red rings represent the location of the fossil galaxy
“It’s great to ‘see’ this galaxy,” said author and astrophysicist Ricardo Schiavon of John Moores University in Liverpool.
“It’s really small in the cosmological context – only 100 million stars – but is almost half the mass of the entire Milky Way halo.
In their study, Dr Schiavon and his 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 at through the Milky Way.
“To find a fossil galaxy like this, we had to look at the detailed chemical makeup and motions of tens of thousands of stars,” Dr. Schiavon explained.
“This is particularly difficult to do for the stars in the center of the Milky Way, because they are hidden from view by clouds of interstellar dust.
“APOGEE allows us to pierce this dust and see more deeply than ever the heart of the Milky Way.
Experts in Liverpool 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”, after the hero of ancient Greek mythology – represents a third of the spherical “halo” of stars and gas in the Milky Way. In the photo, the location of Hercules seen through the map of the Milky Way
“Of the tens of thousands of stars we looked at, a few hundred had remarkably different chemical compositions and velocities,” said article author Danny Horta, also of Liverpool John Moores.
“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 precise 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 peers, as “most similar massive spiral galaxies have had much quieter early lives.”
“As a cosmic home, the Milky Way is already special to us, but this ancient galaxy buried inside makes it even more special,” concluded Dr Schiavon.
The full results of the study were published in The Monthly Notices Of The Royal Astronomical Society.
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