Astronomers have discovered evidence of a cataclysmic collision that occurred 8 to 10 billion years ago between the Milky Way and a galaxy known as the Sausage Galaxy. This collision completely changed the Milky Way and helped to create its distinct outer halo along with its inner bulge.
After hurtling into the Milky Way, the dwarf galaxy known as the Sausage did not manage to survive the mighty impact that it caused. The Sausage ended up drifting apart, as Phys.org report, and the remnants of this ancient galaxy can still be seen in our galaxy today.
The University of Cambridge’s Vasily Belokurov explained that this event “ripped the dwarf to shreds, leaving its stars moving in very radial orbits” that are extremely thin and almost like needles. The path of the stars moved them “very close to the center of our galaxy. This is a telltale sign that the dwarf galaxy came in on a really eccentric orbit and its fate was sealed.”
Cambridge graduate student GyuChul Myeong headed up much of the new research on the collision after his team analyzed data taken from the European Space Agency’s Gaia satellite. This satellite has been able to study the Milky Way’s stars and map them over time, allowing astronomers to better understand their trajectories and history.
The dwarf galaxy that smashed into the Milky Way has been given the name of the Gaia Sausage because of the orbits that its stars ended up taking after the collision, according to Wyn Evans of Cambridge.
“We plotted the velocities of the stars, and the sausage shape just jumped out at us. As the smaller galaxy broke up, its stars were thrown onto very radial orbits. These Sausage stars are what’s left of the last major merger of the Milky Way.”
Even though the Milky Way continues its own collision course with other galaxies like Sagittarius, the collision with the Sausage Galaxy was much more profound because of its size. When astronomers looked at the stars, dark matter, and gas of its galaxy, they determined that its total mass would have been 10 billion times that of our own sun.
After the collision, the debris that was left over from the Gaia Sausage ended up drifting into the inner area of the Milky Way, which is why we have the halo and bulge in it that we do today.
Astronomers are able to run simulations of a collision similar to what would have happened between the Milky Way and Sausage Galaxy which show that the stars left over from the Gaia Sausage would have had orbits that were stretched out as a result, according to Alis Deason of Durham University.
“The Sausage stars are all turning around at about the same distance from the center of the galaxy.”
The new research on the collision between the Milky Way and Sausage Galaxy has been published in Monthly Notices of the Royal Astronomical Society.