The Milky Way has already engulfed large galaxies

Our team of Dutch astronomers concludes that our galaxy, the Milky Way, would have merged with another great system in its infancy.

It is well known that galaxies sometimes eat a neighboring system. Previously, it was thought that only the giants galaxies had done, but recently it appeared that small galaxies could also fuse with neighboring galaxies. And our own Milky Way also seems to have been a "cannibal".

Astronomers, led by astronomer Amon Helmi of Groningen, have recently discovered, with the help of the GAIA space telescope, that the Milky Way in its youth has another great galaxy.

See also: "The Milky Way Center contains thousands of black holes"

Club stars on strike

Since the launch of GAIA in 2013, the positions, the movements and clarity that it occupies determine more than a billion stars with great precision. The main objective of the mission is to create the largest and most accurate three-dimensional map of our Milky Way.

Astronomers used GAIA observations for 22 months and examined seven million stars whose positions and 3D velocities were available. . The team quickly noticed a large number of stars – about 33,000. Their elongated orbits stretched in the opposite direction to that of the other billions of stars of the Milky Way. , including our sun.

Opposite Orientation

This could mean that these stars once belonged to another galaxy. This is true. "The Milky Way disk was probably created as a sort of vortex, in which the gas contained in a huge flat disk revolves around the center," says Koen Kuijken, professor of galactic astronomy at the Observatory. of Leiden and not involved in the study. "From this gas, stars form, which have the same rotation."

"A group of stars turning in the opposite direction around the center does not belong to it, which is why we assume that they were subsequently submitted separately. the second galaxy came from the contrarian direction, but it could also have been directed towards the Milky Way – in this case it had been more difficult to identify. "

Coincidence? [19659009] But is not it a coincidence that some stars are turning? "There is an infinite number of possible uses around the Milky Way, the disc and in the same sense as the others, not at all in the disc or the other way," says astronomer Helmer Koppelman ( University of Groningen), one of the researchers

"The fact that we have different groups of stars.The discovery on the same orbits around the Milky Way indicates that these stars have the same origin: a melted galaxy. our research, we have studied by far the largest group of stars in an opposite orbit. "

That this group of stars came from a different system, concluded the researchers after having simulated previous simulations of the fusion of two large galaxies with the GAIA data, and they correspond.

Transversal Stars

In addition, these "transverse" stars have a different chemical imprint than the other billions of stars of the Milky Way, which also indicates that they are at least 30% higher. ;origin. from another galaxy. Stars that once belonged to another system now form the inner halo of the Milky Way: a kind of spherical space made up of ancient stars surrounding the disk of the Milky Way.

In addition, analyzes showed that the galaxy the Milky Way had been swallowed ten times smaller than the current galaxy. Billions of years ago, the Milky Way was much smaller. The researchers therefore estimated that the ratio was 4: 1 at the time (the other system was therefore four times larger). Amina Helmi describes as violent the meeting between the two galaxies and "the milky way well shaken"

. Sources: Nature, University of Groningen via EurekAlert !, Press Release

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