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The researchers discovered an ancient and dramatic frontal collision between the Milky Way and a smaller object, nicknamed the "Sausage" galaxy.
The cosmic accident was a milestone in the history of the Milky Way and reshaped the structure of our galaxy, shaping its inner bulb and its outer halo, astronomers report in a series of new articles .
Astronomers propose that about 8 billion to 10 billion years ago, an unknown dwarf galaxy broken in our own Milky Way. The dwarf did not survive the impact: it quickly collapsed and the wreckage is now all around us.
"The collision shredded the dwarf, letting his stars move in very radial orbits" that are long and narrow like needles, says Vasily Belokurov of the University of Cambridge and the Center for Computational Astrophysics at the Flatiron Institute of New York. The paths of the stars take them "very near the center of our galaxy." It is a telltale sign that the dwarf galaxy has entered a truly eccentric orbit and that its fate has been sealed. "
The three new items in monthly records of the Royal Astronomical Society in Astrophysical Journal Letters and arXiv.org describe the main features of this extraordinary event
Researchers used Gaia satellite data of the European Space Agency. This spacecraft has been mapping the stellar contents of our galaxy, recording the journeys of stars as they travel across the Milky Way. Thanks to Gaia, astronomers now know the positions and trajectories of our celestial neighbors with unprecedented accuracy.
The stars' paths of galactic fusion have earned them the nickname "Gaia Sausage," says Wyn Evans of Cambridge. "We have traced the velocities of the stars, and the shape of the sausage just jumped in. As the smaller galaxy separated, its stars were thrown into very radial orbits. which remains of the last major merger of the Milky Way. "
When looking at the velocity distribution of stars in the Milky Way, the stars of the Sausage galaxy form a characteristic sausage shape. This unique shape is caused by the strong radial movements of the stars. As the sun is in the center of this huge cloud of stars, the cast does not include the slow-moving stars that are currently making a U-turn towards the center of the galaxy.
Sergey Koposov, a member of the McWilliams Center of Carnegie Mellon University for Cosmology, studied the kinematics of sausage stars and globular clusters in detail
The Milky Way Continues to Collide with D & C Other galaxies, such as the clbady dwarf galaxy of Sagittarius. However, the galaxy of sausage was much more mbadive. Its total mbad of gas, stars and dark matter was more than 10 billion times the mbad of our sun
Is the Milky Way really weird?
When the Sausage crushed into the young Milky Way, its trajectory piercing caused a lot of chaos. The Milky Way disk was probably inflated or even fractured following the impact and should have grown back. And sausage debris was scattered all around the inner parts of the Milky Way, creating the "bulge" in the center of the galaxy and the surrounding "stellar halo".
Numerical simulations of galactic mashup reproduce these characteristics, says Denis Erkal of the University of Surrey. In simulations conducted by Erkal and his colleagues, stars from the Sausage galaxy enter into stretched orbits. The orbits are elongated by the growing disk of the Milky Way, which swells and becomes thicker after the collision.
Evidence of this galactic remodeling is visible in the trajectories of stars inherited from the dwarf galaxy, says Alis Deason of Durham University. "The sausage stars are all about the same distance from the center of the galaxy." These U-turns make the stellar halo density of the Milky Way dramatically decrease where the stars turn.
Nice for Deason, who predicted this orbital battery nearly five years ago. The new work explains how the stars fell into such narrow orbits in the first place.
The Milky Way ate 11 more galaxies
The new research also identified at least eight large spherical groups of stars called globular clusters that were brought into the milky way by the sausage galaxy. Smaller galaxies usually do not have their own globular clusters, so the galaxy of sausages must have been large enough to accommodate a collection of clusters.
"Although there were many dwarf satellites falling on the Milky Way during his lifetime, the greatest of all," says Koposov
Source: Carnegie Mellon University
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