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 included in its "halo," claim astronomers
- Experts analyzed the composition and movement of tens of thousands of stars
- This enabled them to identify the hidden remainder of the galactic collision
- The "fossil" that is located near the center of the Milky Way was called Heracles
- Such collisions and fusions create large galaxies
Another galaxy was added to our own after a collision with the Milky Way about 10 billion years ago, astronomers have shown.
Experts from Liverpool found this galactic "fossil" hidden in the depths of the Milky Way by analyzing the motions and composition of tens of thousands of stars.
This cosmic remnant – named "Heracles" after the hero of ancient Greek mythology – makes up a third of the spherical "halo" of the Milky Way of stars and gas.
The remains of a number of ancient galaxies had already been discovered in the outer halo of the Milky Way – in fact, sizeable galaxies are being built through mergers.
To find such earliest fusions, however, the most central part of the Milky Way's halo must be analyzed – which is buried deep in the disk and bulge of the galaxy.
Another galaxy was added to our own after a collision with the Milky Way about 10 billion years ago, astronomers have shown. The picture shows an artistic impression of the Milky Way as it can be seen from above. The red rings represent the location of the fossil galaxy
"It's great to 'see' this galaxy," said paper writer and astrophysicist Ricardo Schiavon of Liverpool John Moores University.
"It's really small in a cosmological context – only 100 million stars – but it is almost half the mass of the entire Milky Way halo."
In their study, Dr. Schiavon and colleagues have collected data from the Apache Point Observatory's Galache Evolution Experiment [APOGEE] that has collected data on more than half a million stars in the Milky Way.
"To find a fossil galaxy like this, we had to look at the detailed chemical makeup and motion of tens of thousands of stars," said Dr. Schiavon.
"This is particularly difficult for stars in the middle of the Milky Way, because they cannot be seen through interstellar dust clouds."
"APOGEE lets us stab through this dust and look deeper into the heart of the Milky Way than ever before."
Experts from Liverpool found this galactic "fossil" hidden in the depths of the Milky Way by analyzing the motions and composition of tens of thousands of stars. This cosmic remnant – named "Heracles" after the hero of ancient Greek mythology – makes up a third of the spherical "halo" of the Milky Way of stars and gas. Depicted the position of Heracles on the plane of the Milky Way
"Out of the tens of thousands of stars we looked at, several hundred had strikingly different chemical compositions and velocities," said paper writer Danny Horta, also of Liverpool John Moores.
"These stars are so different that they could only come from another galaxy."
"By examining them in detail, we can pinpoint the exact location and history of this fossilized galaxy," he said.
Based on their findings, the team came to the conclusion that the collision between Heracles and the Milky Way "must have been an important event in the history of our galaxy".
This, she added, makes the Milky Way unusual among her colleagues, as "the most similar massive spiral galaxies had much quieter early lives".
"As our cosmic home, the Milky Way is already special to us, but this ancient galaxy 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.