Melkweg swallowed a small system – NRC

By our employee Eddy Echternach

About 10 billion years ago, the galaxy – at that time still very young – came up against a smaller congener. This event had a serious impact on the structure of our galaxy. In the milky way, hundreds of millions of stars galactic invader, called Gaia-Enceladus, are also left behind.

This stems from new research based largely on Gaia data. This European satellite, launched in 2013, measures the positions, speeds, brightness and colors of more than a billion stars. Astronomers hope to better understand the origins of the Milky Way. The research report was published Thursday in Nature .

In the opposite direction

As part of the research, a group of 33,000 stars was discovered that differs in a different way from the approximately 200 billion "native" stars. In this way, they move in opposite directions around the galactic center, relative to our sun and almost all the other stars of the Milky Way. In addition, they present a characteristic chemical composition, which provides information on their earlier history.

"The first stars of a galaxy that have enough mass explode very early, spreading their matter across space," says Amina Helmi, director of research, research director at the 39 Kapteyn Institute of the University of Groningen. "All kinds of heavy elements are released during these supernova explosions.As time goes by, more and more supernovas of a different type are added, which mainly disperse even heavier elements, including the Iron. "

This process means that later formed stars have an increasing iron content. This is also reflected in the deviant moving stars that Helmi and his team discovered. These stars have very different compositions, which proves that they were not born at the same time but spread over a longer period. In addition, their chemical "fingerprints" indicate that they were born in a galaxy different from ours.

The Helmi team comes to the conclusion that Gaia-Enceladus has about 600 million solar star masses. These stars have now been distributed across the galaxy. According to co-author Helmer Koppelman, who does his doctoral thesis at Helmi, the red dwarf star Ross 451 with a distance of 80 light-years is the closest to the couple.

10 billion years ago

Astronomers estimate that the collision between the Milky Way and Gaia-Enceladus occurred about 10 billion years ago. It's less than 4 billion years after the birth of our universe. "We infer that, from the youngest stars' age – these are the stars with the highest iron content," says Helmi. "This shows that the youngest stars of Gaia-Enceladus are younger than those of the thick disc of our Milky Way."

The galactic system of the Milky Way actually comprises two components: a thin disk and a less densely populated housing which the thick disk is mentioned. The latter contains about 20% of all Melkweg stars.

"One of the most interesting aspects of this research is that you see that when Gaia-Enceladus merged with the Milky Way, there was already a record and that record reacted violently to the sound. event and became thicker, "says Helmi. "But we do not know for sure if all the stars we see now in the thick disc already existed.It is quite possible that during the fusion, new formations of stars in the Milky Way began." 19659003] According to Helmi, there were no subsequent collisions with galaxies the size of Gaia-Enceladus – only the smaller ones. However, large mergers may have existed before. "It will be a little harder to prove it, but it's impossible," Helmi said. "I would not be surprised if this already matches the current Gaia data."