Our galaxy appears to be the way we see it today because of a brutal encounter with an object called the Sausage Galaxy. Logically we are not talking about cosmic processed foods, but about the remains of a small galaxy that crashed into the Milky Way billions of years ago, leaving behind a mess of stars with rather unusual orbits.
So where does the name “sausage” come from? The astronomer at the University of Cambridge (England) Wyn Evans claims that it all came down to the paths left by the stars after the impact. “The sausage shape just jumped at us when we saw the trajectories of the stars,” says Evans. “These sausage stars are what remains of the last great Milky Way merger.”
The history of the collision
Using data from the European Space Agency’s Gaia spacecraft, astronomers uncovered scientific evidence indicating an ancient head-on collision between the young Milky Way and a smaller body called the “Sausage” galaxy, a cataclysm that helped define the structure of the Earth. home to Earth. space, shaping the galaxy’s inner bulge, its outer halo, and adding at least eight massive globular clusters.
The smaller dwarf galaxy did not survive the encounter, rapidly falling apart as its stars merged with the Milky Way and reshaped it.
Vasily Belokurov of the University of Cambridge and the Center for Computational Astrophysics at the Flatiron Institute in New York City (USA) claimed that the collision “tore the dwarf object apart, leaving its stars moving in very radial orbits, carrying them away. very close to the center of our galaxy. This is a telltale sign that the dwarf galaxy went into a really eccentric orbit and its fate was sealed. “
Collisions with smaller galaxies continued later , that is, our galaxy has continued to collide with other galaxies, such as the “insignificant Sagittarius dwarf galaxy”, but the ‘Sausage’ was much more massive: 10 billion times the mass of the sun when its gas, dust, stars, and dark matter are included. When it crashed into the Milky Way, the disk of the galaxy likely swelled or even fractured upon impact and would have had to regrow.
The stars of the ‘Sausage galaxy’ are all rotating the same distance from the center of the Milky Way
The computer simulations reproduced the features described by the researchers, showing stars from the sausage galaxy entering stretched orbits similar to those seen in the Gaia data. The simulations show those increasingly elongated orbits in the Milky Way’s growing disk, which swells and thickens after the collision.
“While there have been many dwarf satellites falling into the Milky Way throughout its life, this was the largest of all,” said Sergey Koposov of Carnegie Mellon University.
The collision is described in various articles published in The Royal Astronomical Society, The Astrophysical Journal Letters and arXiv.org.
Reference: V Belokurov et al, Co-formation of the disc and the stellar halo, Monthly Notices of the Royal Astronomical Society (2018). DOI: 10.1093 / mnras / sty982
Image credit: V. Belokurov (Cambridge, UK); Based on image by ESO / Juan Carlos Muñoz
