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The remains of a powerful collision between the Milky Way and a smaller galaxy, which occurred billions of years ago, are still visible today.
An international team of astronomers discovered that some stars travel in a particular orbit near the center of the Milky Way are the remains of a face-to-face encounter with a dwarf galaxy called Sausage.
The cataclysmic crash is one of the greatest moments in the history of the Milky Way, according to experts. Although the galaxy has merged with a dozen of its satellites since its creation, this particular fusion has reshaped the structure of the Milky Way, creating the inner bulge in the center and the spherical halo surrounding the outer edges.
Sausage galaxy
About 8 to 10 billion years ago, a dwarf galaxy penetrated the Milky Way frontally. The smaller galaxy did not survive the accident because the strong gravitational force from the Milky Way lacerated it.
The researchers however found evidence of the collision in the form of stars traveling in long, narrow orbits near the galactic center. These sausage-like orbits, which gave its name to the galaxy, are called radial orbits
"This is a telltale sign that the dwarf galaxy has entered a truly eccentric orbit and that its fate has been sealed," explains Vasily Belokuro. University of Cambridge
The researchers came to their conclusions after thoroughly studying the data collected by the ambitious Gaia mission of the European Space Agency. The goal was to collect as much information about the positions and trajectories of the Milky Way's millions of stars and to create a three-dimensional map of the galaxy based on the data collected.
The details of the study are published in three articles. in the monthly records of the Royal Astronomical Society, the Astrophysical Journal Letters and the pre-printed site ArXiv
Gaia Sausage
Using Gaia data, researchers were able to badyze the speeds of the stars and trace their trajectories. They found a distinctively sausage orbit, prompting scientists to name them Gaia Sausage stars.
"These sausage stars are what's left of the last great merger of the Milky Way," says Wyn Evans, also of the University of Cambridge
The Milky Way continues to gobble up small galaxies in its vicinity. There are nine dwarfs in orbit around the galaxy, but the Milky Way is currently engulfing the Sagittarius dwarf galaxy.
In the 100 million years to come, the gravitational pull of the Milky Way will tear Sagittarius in a similar scenario. to what happened to the galaxy of sausage.
Sausage, however, was probably more potent than Sagittarius. Despite its size, it caused a lot of damage in the Milky Way after the collision, causing swelling of the galactic center and scattering of the wreckage along the inner parts of the galaxy. The researchers believe that it is this collision that has shaped the Milky Way in the cosmic structure that it is today.
They also found eight globular clusters left behind by the accident. Globular clusters are ancient spherical clusters of stars that are usually found in large galaxies. Although sausage was a dwarf galaxy, scientists believe that it had to be big enough to house its own cluster of stars.
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